I like playing against real humans because they are more interesting to play against (or with), but, I hate playing multi player when people act like idiots. When I'm playing MMOs, I like to solo a lot while levelling and just group for PVP - people even complain that you won't group with them, when you a)don't know who they are and b) there are hundreds of other people out there they could group with.

Humans might be nicer to fight, but sometimes they're too much hassle to have to deal with :-p