I, for one, prefer solo playing. I play to relax. Some of the best games out there are one-player games.
When I do play with other people, I try to do it for socializing. This is why I don't like Super Smash Bros.; the controllers make no sense, nobody explains to me how some thigns will kill you that (in my mind) SHOULDN'T, and I swear some people go AFTER ME knowing that I'm a noob. I don't play socializing games to get my ass kicked; that's not playing.
As for online play, there aren't that many games out there that I like that ARE online games, and those that are I don't do anyways. This is mainly because my PS2 has yet to be connected to the net, and I'm sure that the few games that I'd consider doing online gaming with are no longer popular enough to even bother with.
I honestly have no real reason to do online gaming.