Chris, without a second thought. Because he's hot.
No... I mean, yes, he is hot, but I also enjoy his story more, it lays the groundwork for his future relationship with Wesker, who doesn't have the same obsession with Jill as with Chris, and I also like Rebecca more than Barry. Otherwise, the scenarios play out pretty much the same way, so there's not much to prefer about the one or the other, Chris's smaller pockets can be annoying, but Jill getting more weapons and ammo types and subsequently having to balance more stuff in her inventory kind of makes up for that. I'd say Jill's scenario is still the easier one, but overall, I prefer Chris's.
Also, every time I play as Jill, I'm forced to let Barry die, because I can't handle her stupidity in the scene that follows if he survives. I don't want to kill Barry, though.