Usually good. What can I say? I like to be the hero. The only games I ever played evil in for my own enjoyment (rather than just achievement completion or to see how the story changed) were the Fable games because I hated all the annoying NPC jerks too much and Fallout 3, because, well, that actually enabled some pretty creative roleplaying as a cannibalistic serial killer, and that was awesome.
I played good and neutral in Fallout 3 as well, but I had a fantastic experience doing the evil roleplaying, because, essentially, it resulted in there being a story and character growth. I had started off as a not-particularly villainous character, but then a few mistakes led to my character spiraling off the deep end. Plus, a lot was implied in the dialogue that the Wanderer turned out evil because s/he resented being abandoned by their parents, and then grew to distrust and hate mankind.
That actually turned out to be more interesting than the good choices, and was better than most evil choices in games, which essentially involve the character being a dick for the sake of it. But, yes, generally speaking, if there is a morality choice in games, my first instinct is always to take the good path. I find it more rewarding when you don't alienate your party, which evil choices normally do.