if you ask me, the hardest character in this game is aba. hos being second and past that it's a crapshoot.
what makes them both hard is that they're momentum based characters; one mistake with either one of them and you've lost. hos less than aba, because he can still do stuff without charge meter (though he's a weaker character all around, at least you're given a few more chances than say, with aba).
it's like the guy who said the hardest part of playing johnny is training mode; it's not that training mode isn't hard, but knowing how to poke (and how to move) is so much harder that many people switch mains because of it.
eddie, who many say is the hardest character, is the exact opposite. the hardest part of playing eddie is learning all the unblockable setups, and once you get his footsies down every match becomes training mode unless your opponent knows the matchup at least as well as you do.