PC, because my PC is a sixy beast (I just got me a GTX460). And, it's hooked up to my very sixy HDTV. Also, because I can pull off headshots like a pro with a mouse, but I can't hit a Behemoth's backside from 10 feet away with a controller.
RE: the PC vs console graphics questions, it isn't even just about the hardware--PC version has higher-res textures (or at least, the ability to run the textures at higher quality settings).
I've killed everything in the game free aim on my PS3 using a controller, I guess it's all what your used to.
But after a while I started using VATS, i was hooked, I love the slow motion affect so you can see the blood mist hang in the air for a few seconds after i pop a head with with my beloved Victory Rifle. And all this is just testament to how great this game is! You can play it on anything you want however it pleases you to do so and they make it so you can change anything you want whenever you please brilliant!!!
I say Oblivion and Fallout are the most entertaining game experiences I have ever seen, and I've been gaming since Pong.