To me, at this stage of the game I would say PC. There are very few true exclusives to the 360 vs the PC. PC has more overall functionality. Dependent on your arrangement With a simple wireless mouse & keyboard, (and if you are a stickler like I am, you can get a 360 PC wireless controller transponder) you can connect a PC to a modern HDTV and use in the consoles home turf the "on the couch" layout. (actually thats one of the very very few things that Windows 8 makes easier)
Dont get me wrong, the 360 is a good console in its own right. But I feel you have infinitely more gaming options,(especially old games thanks to GoG, and indie games thanks to Bundles.... Fuck steam as it is wrongly over hyped) more multitasking options, more longevity and use out of a PC than you will out of a 360. So Unless you are REEEEEEEEEEEEEEEEALY into Halo and/or Kinect games (and Kinect can be used on PC TOO) it just makes the most practical sense to go with the more adaptable platform.
Edit: Personal comparison... My Home entertainment center in my living room is 3 42 inch LEDs stretched to surround mode with the center being 3d enabled., I have 360, PS3 and PC connected. My physical library of games is predominantly 360 (pushing 50 vs PS3s 10), but my PCs digital library of games is well over 100. Honestly I would say, I have used the 360 only in the last year, right at 500 hours. The PC in comparison has been used closer to 5000 hours in that same time. Just my situation, but simply illustrating one individuals level of use comparatively.