So I have this problem.
Usually I have to decide between X360 and PC versions of the same title. On the one hand, I know the PC version might look better, but the XBOX versions is usually guaranteed to be stable (that is to say built specifically for the hardware as opposed to PC where it is built within a range). I have a decently powerful machine, so I rarely have to wonder if the computer can play the game, but moreso how the game will play on the computer.
Then there is the question of achievements. (None of which would be an issue if Games for Windows would tie in with my Live account). Xbox live keeps track of games I've played and what I've done in those games, and that's something I love. I lose that on the PC.
But it sometimes comes down ot price. On average the PC version of a game is $10 less than that console. That's not a while lot, and usually won't break the call, but every now and then Steam goes and does things like this. This is the kind of pricing on games that really changes the market, and I love Steam for it.