Reincarnation is the easiest, as the author didn't need to write the "first contact" interaction plot like Transmigration or Summoning.
Its also helping the main character to learn how to live in the Otherworld without much problem and experiment, as they've been grown there their whole lives.
The only negative part about this is that some reader can't stand Body-snatching possession related crime. Plus the fact that 20-30-40yo man acting like a child after reincarnation isn't accepted and considered a flaw, as people forgot that mental regression and retardation is a thing.
Plus author usually just ignore the hurdle of changing daily routine and way of living abruptly, not to mention the existential crisis and potential split personalities if the memories were combined.