There are achievements on the PC version as well. Though they obviously don't have any other use outside the game unlike a gamerscore. As others have said, you get better graphics if your computer can handle it, the texture pop-in exsits but it's minimal compared to the 360 version, the keyboard and mouse will give you better control in combat, and I believe the bring down the sky DLC was free for the PC version (don't know about this new one).
You can't go wrong either way. If your computer can handle it, then I'd be tipping the scale to the PC, but that's just me.







