I'm busy devising a typical vampire universe. As such, the oldest vampire is the most powerful, because he carries the source of them all. The oldest vampire is basically the god with cosmic powers who perceives things beyond the Local group. Hence he's nearly omnipotent. And by the definition of earthlings also omnipresent.
Even the oldest actually known to other bloodsuckers vampire is capable of destroying the planet. The true oldest vampire is over ten times older than that and pretty much unfathomable. He's prolly capable of manipulating matter beyond the reaches of the galaxy. He simultaneously reads the minds of every living being on the planet. He is aware of everything that takes place. But all of that is still but a fraction of what he perceives at any moment. That is why he's incomprehensible.
Even he's not truly eternal. He's also several times younger than his "race", as vampires have existed for nearly as long as humans have. He's no longer an actual vampire in a traditional sense, as he doesn't drink blood or anything else. Nor does he require a physical body. He’s pretty much a ghost with a presence spread all across the Earth and beyond.
He hasn’t really been seen during the holocene, so he is just a myth. He had also transcended beyond the comprehension of other vampires tens of thousands of years ago. That’s why he’s uninterested in our world. He’s more occupied with the developments a Cluster away. The only reason he might actually meddle in the Earth’s affairs is if humanity or vampire-kind came to the brink of extinction. And even then, maybe not.
He doesn’t really appear or play any relevant role in my story.
The strongest when pushed over the edge is probably my MC. I’m not original at all, I know. MC is in possession of ancient blood of a special kind, but is unaware of that. Also, MC’s sire died right away. So, MC’s got no clue about how to properly utilise powers and what kind of powers there are to begin with. All of that would be meaningless against an actual ancient vampire of say half a millennium yo or so. But a curious trick against a normal opponent anyway.