I'm generally a healer or someone who doesn't like things to die. In an RPG, I'm generally a healer, such as in Final Fantasy XI- White Mage or Scholar, or in the short time I played World of Warcrap, I played mostly Priest before I uninstalled the game, spat on the CDs, and handed them back to my friend.
Same with in class-based FPS games. In TF2, I play Medic a lot, sometimes Spy or Heavy if I feel like getting some vengeance. Command and Conquer Renegade, even though it doesn't score me a lot of points, I have a real difficulty killing people, so I usually choose Engineer or its respective classes.
In RTS, I usually turtle because I don't like my pixelated infantry getting killed. I've read and heard a lot of war stories, so I try and avoid death as much as possible. Guaranteed my kill/death ratio is higher than anyone elses (that isn't to say I win a lot, though). I also make sure all of my guys are like fully repaired before I send them in any major skirmish.
I also like being able to use my opponent's abilities against them. In Smash Bros Melee, I loved Fox and Falco because their reflectors consistenly bounced my friend's fully-charged Samus B attack back at him. In Final Fantasy XI, my favourite job is Blue Mage. Learning attacks that monsters spam on you time and time again, then being able to use them right back at them... ooh, it feels good. {Bomb Toss}+{Self Destruct}{You can have this.}{death}{Good bye.}{See you again!}