PC for sure. I love the all-in-one sort of aspect with it (you don't have to buy a seperate console, controllers, games, memory cards, etc.)
You just buy a good solid computer, you can do everything with it. Watch TV with a TV Tuner, play many great games, and then everything else a computer can do. If I was to go with a console, though, it would definitely be a PS3.
I picked Xbox 360 just cause I love playing it. The online networks are GREAT some noobs here and there but where aren't there any noobs these days? lol and my second pick would definitely be a PC since I do most of my work on a PC and I just love having a Windows Computer, Linux for other reasons
Xbox 360, I'm more familiar with how to play it. Though if I could I would resort to PS3. It also depends on the game like the Sims, I prefer on my PC.