It really depends on a number of factors, and all of this is based upon the characters that I have actively introduced in my stories for the world I've created, or otherwise actively mentioned within the lore stuff that is readily available.
Are the characters in-question travelling to Elaria? Are they only competing in the lower dimensions of the cosmology (Earth, Elaria, Shadow Realm)?
Are they crossing the veil into Kur? Are they entering the Higher Dimensions?
Are they fighting one-on-one, or in groups/teams?
It does matter, but with the way my story is set up, no single character can "solo" everything, or anything. Teamwork is an absolute necessity, even at the mundane level. For example, those entering the second dimension (Elaria) are all subject to its universal laws [Rank, Class, Level, Skills, Techniques, etc etc]. Those crossing the veil into Kur, are likewise subject to Eshraea's domain and its laws, and if we are including Eshraea's domain (Kur) the answer becomes an immediate "Nobody", because Eshraea is on a completely different scale any just about every other fictional setting or cast.
The same would be the case for the Higher Dimensions as well, which are the realms of literal Gods and Goddesses.
So, I'll take this under the premise that the characters crossing over are crossing into the world of those they are fighting. (Thus, the external characters crossing into the world of our stories to fight our characters within those worlds). Under that premise, the following presentations are under the understanding that the characters are fighting in Elaria, and thus, must abide by the universal laws that govern reality within Elaria.
I'm also not delving into any speculations over how the engagements would go in alternate worlds or locations. Especially the Higher Dimensions of my multiversal setting [The very laws of reality are shaped by whatever God or Goddess governs the region, and depending on how close to the borders a fight occurs, the stipulations of it can change drastically and without warning.)
If we're talking one-on-ones, strictly the lower-dimensional cast, it becomes a much closer struggle, and specifically, whether the other characters have some means of actually removing enchantments in their kit. If they don't, then they'll run into trouble trying to deal with Sylvia or Xu Wing. The former of the two has virtually zero offensive capability, but crazy-good "healing factors" in her spells and enchantments, and it becomes a contest of stamina, which she'll probably win almost 90% of the time. Xu Wing is a Necromancer and her kit includes insane self-healing abilities as well as insidious curses, debuffs, condition-spam, and life-steal. She's kitted out to win most battles of attrition, and excels in making a fight into a battle of attrition. Lapis and Lazuli (#17 & #18 respectively) would be the only ones able to outlast Sylvia or Xu. But in the case of #18 and Sylvia, they'd probably end up calling it a draw and spending the rest of the time talking about fashion, or going out to the spa to relax.
Droskar and Rowan are also incredibly formidable fighters (and the only ones in the cast so far who actively enjoy fighting) but while Rowan is the stronger fighter, Droskar would be the one to last longer in a fight. They'd both probably end up losing to someone like Superman, Kakarot, or Vegeta though. [It'd be a hell of a fight, sure, and they'd probably end up as friends after Sylvia's done patching everyone up].
Since Teamwork is key however, the only truly fair contests would be teams-vs-teams.
So, Knights of Avalon (Lucius, Droskar, Calindra, Rowan, Xu Wing, Sylvia, Jacky + Bel) -vs- Justice League - This would be a major toss-up, and it would come down to which side runs out of steam first. Superman overpowers most of them with ease, but Sylvia's healing spells can offset that. He is also known to be 'vulnerable' to magic, which is what half of the cast uses. In the end, though, I'd have to give it to the Justice League. Superman (Kal-el) is just in a whole other league for stamina too. He'd be able to outlast even Sylvia's crazy healing magic until she runs out of mana, and nobody in the Knights (that was formally introduced) has the firepower to put him down for the count, especially with the support of the rest of the Justice League.
Knights -vs- Avengers - Depends on whether or not Wanda (Scarlet Witch) is able to actually start using her magic. She is still only human, after all, and Bel excels at anti-caster combat. If Wanda is able to, she's going to carry. Otherwise, it'd be a lot closer. I'd have to give it to the Knights here (if they manage to take down Wanda and Strange quickly enough), because Lucius' strategic approach would be far more well-suited to dealing with this group, than the likes of Superman. His spells would be far more effective here as well, and would likely be the deciding factor.
Knights -vs- Z-Fighters - The main point of contention here, is that the Z-Fighters are all basically the same 'class'. They're all "Monks" in the world of Elaria. Powerful ones, absolutely, but they're all monks. That single factor would prove to be their downfall in a team-battle. The imbalance would prevent them from being able to form a cohesive unit capable of countering or resisting the combined abilities of the Knights with their varied classes and expertise. One-on-One, the Z-Fighters are stronger. No doubt. But that isn't actually the deciding factor here. It is the kits they bring to the fight. None of them have any real defense against magic like Lucius' Shadow Binding, and none of them have any hard-counters to Sylvia's or Xu's enchantments, or any hard counters to Bel's Dance of Shadows. It's for that reason, that the Knights get the win here.
Knights -vs- Naruto/Boruto - Surprisingly, the Naruto/Boruto cast are actually better equipped for this kind of fight than the Z-Fighters in cast-versatility, but they are still lacking any hard-counters to Sylvia's magic and enchantments in particular, as well as some of Xu's curses. Sylvia's healing magic, especially with Lucius' support, will outmatch virtually anything the Naruto cast can throw at her. The difference is in the extent to which the healing elements come into play here, that would shape the outcome of the fight. Sylvia can revive her fallen comrades, as well as revive herself (Her Phoenix Flames Enchantment). The Naruto cast have no hard-counters to that, and while some of them have healing techniques, they aren't nearly as effective, or as quick, as her magic. Additionally, between Sylvia and Lucius, the Knights have hard-counters to just about everything the Naruto cast can throw at them.
Knights -vs- Phantom Thieves of Hearts (Persona Series) - This one is far more one-sided against the Knights. The Phantom Thieves have their Personas (Would be classified as Summons in Elaria), which possess hard-counters to just about every spell and ability that the Knights can bring to the fight. Most prominently the ability to remove magical effects and the ability to bypass defensive abilities (IE: Almighty Attacks). This one comes down to the effectiveness of the group's teamwork, which as close as it is, leans squarely in favor of the Phantom Thieves. Their tactics, and hard-counters would give them the distinct ability to not only prioritize taking down Sylvia, but the means by which to do it. Without her healing support, the Phantom Thieves would eventually secure the win.
What all of this really comes down to is the universal laws that govern Elaria, and their LitRPG system mechanics. All Attributes are hard-capped at 100 (1000 for Health and Mana) + Whatever Class and Ancestry bonuses the character would have to them by default, and these limits can only be surpassed after a character has obtained the Limit-Breaker skill. Which is a conceptual-skill that is the gateway to Divinity and Ascension. The only fictional character that I know of who would rightly enter Elaria with this skill is Superman, as by his character design he conceptually has no limits to speak of. Otherwise, the only way to obtain the skill is undertaking a Hidden Class-Based Quest to unlock the skill. There are no 'hacks' to exceed these limits.
Beyond this, all techniques, spells, and equivalent abilities, are treated exactly as their effects are defined within their source material. The deciding factor in most of the fights comes down to how well the teams can manage their offense and defense, and which sides have hard-counters, or soft-counters to the other team's kit. Sylvia's signature spell, which is a fairly powerful healing enchantment, combined with her healing magic play a huge role in keeping the Knights in the fight, and without any serious hard-counters for it (ability to break enchantments, or remove magical effects), the Knights in Elaria have an exceptionally strong defense that can keep their offensive players in the fight.
If the fight were to take place in Earth; things would go very VERY different. The 'Earth' of my setting mirrors the real world we all know, so all of the real-world laws of physics that govern reality would apply. No magic. No Ki powers. No Chakra shenanigans. Just a bunch of folks flailing angrily at each other. Droskar and Rowan carry hard here, since they actually wear armor, and wield weapons. The rest would drop real quick. Lucius, Sylvia, Xu and Calindra would be dead-weight. Bel with her daggers could do some serious damage, but it equally vulnerable to other armed fighters since her armor isn't really armor. Trunks and Rock Lee would probably fair the best out of their respective casts, on account of actual martial training, and Trunks has a sword at least.
In the Higher Dimensions, it could go from a rap battle to an eating contest, to a dance-off, to a beauty pageant, to a generalized talent show with no real rhyme or reason beyond which deity's domain the 'fight' is happening in at the time, so I'm not even going to bother trying to analyze those shenanigans beyond to simply say Goku wins any and all eating contests without any real competition. Sylvia would probably win in a beauty pageant with some serious competition from Natasha and Lazuli, and Beerus would own the dance-off with his breakdancing moves.
As an addendum, I'd also like to point out that any of the fights between the characters would be incredibly unlikely if those characters did cross into the world, because of their own beliefs, morality, and ethical alignments. They may differ in methodology, but the casts would be far more likely to get along and form friendships, rather than actively trying to kill one-another. (Except maybe the Saiyans and Rowan or Droskar. They'd definitely come to blows in a few 'friendly' matches). Sylvia though, is far happier to just lounge around on her divan and people-watch, or chill and be pampered in the spa, when she's not busy seeing what other kind of mischief she can get into. Basically anything other than actually fighting. Lucius, would spend more time trying to figure out how to incorporate them into his plans to save Saphria, and is certainly smart enough to opt to make friends, rather than enemies, when possible.
Goku would probably revel in the mysterious new world, and all the techniques and skills he'd be able to learn, or the foods he'd be able to try, and of course, all the new challenges he'd get to face by going on a brand new adventure, and would end up dragging the rest of the z-fighters along for the ride. Except Roshi. He'd probably spend all his time creeping on the girls in Sylvia's guild hall, or trying to sneak into the bathhouse or spa.
On the note of how my characters would fare in other universes, that would be subject to those who define the rules governing those settings. Their creators and/or caretakers. I have no authority to arbitrarily decide how my characters, and their spells, techniques, and similar abilities, would function within the setting of other creators.
Also, as an additional addendum, for those who are wondering about it, here's why Eshraea turns the entire question into a moot point, she is the Goddess of Death, the Underworld, and the Afterlife. Omnipotent, Infinite, and Eternal in the truest sense of the words. Her Divinity and Authority govern Life, Death, and the Transmigration of Souls through the multi-dimensional cosmology. Anything that crosses the veil, and enters Kur, is subject to her Divine Authority, and it truly doesn't matter who, what, or how strong, something is at that point, as it belongs to her. Yes, this also includes other deities and divinities. The entire concept of fighting against her is a moot point, where power amounts to nothing in the face of Inevitability. In my setting, she is the singular being who sits at the pinnacle of all that is; for in the end, all will enter into her domain, and her embrace. (Yes, this also includes all of the other deities in my setting; save one, who isn't mentioned formally in any of my works).
