I'll sum it up or I'll be here all day
PC version has mouse/keyboard obviously, though the 360 controls do a good job and are fairly responsive after a few mins or so play about.
The match engine on the PC is clearer (at least on a normal SDTV), the players, pitch and ball are larger and easier to see.
The 360 version trades size (it's got the equivalent of 'small' PC database of players, though there's still *tons*) for speed, it's easily 3-4 times faster than my good PC.
PC version has editor and mod support, while currently 360 version doesn't have an editor and patching news hasn't been confirmed that I'm aware of (though this could change of course).
So it's a bit of a toss up really, I always found the PC version's slow speed and miniture buttons/mouse to be a pain at times so I only use the 360 versions now, but many people swear by the computer version, they're just some of the main point I've picked out.