It really depends on what games you like.
If you prefer console gaming, have a nice TV and stereo system to run an xbox 360 through and like Halo a lot, Xbox 360 would be the way to go. The 360 also has Kinect and several downloadable games on xbox live.
The downside is that you have to pay additional fees for a premium xbox account to play online multiplayer games.
If you go the PC route, a PC can be more money up front, but you also have more options; upgrading graphics cards, adding a blu-ray drive, many many games available for PC are also on PS3 or Xbox 360.
If you prefer gaming with a mouse, go PC. If you prefer gaming with a controller, PC or 360 are both options.