well, i have a xbox 360 and a gaming pc, and in my honest openion, both are very powerfull, xbox 360 runs a xenon tri core, 3.4 ghz processor, and a equally good gpu,
but my computer is running a 9800gtx with a dual core e7400, which cost 5 times the price of a xbox 360,
so unless u have a budget of around 60k, not to mention the accesories, and displays, and ur a hard core gamer...
dont go for a pc,
also my pc runs a DX10 which has way better shaders and texture filtering, than the DX9 used by ps3 and xbox 360, also there is no end to a computers performance, but consoles will max out at a point,
hope this helps