In the Pokémon anime, which one of Ash's Pokémon (other than the Pokémon that have been in more than one region with Ash, unless you re-count the number of faints for each region, and not including Raticate or Aipom or any of his unofficial Pokémon) has fainted the most?
I'm not going to bother checking every single episode, since I have better things to do with my life.
However, I can say with a 90% certainty that it's Pikachu. Not because it's weak, but because he has stayed with Ash the whole time, much more longer than any other of Ash's pokemon. So he's battled more and likely to have lost more.