Wasnt a fan of ATI's drivers either. I got a 4870 around the time they came out, loaded up Crysis Warhead, same settings as my previous Nvidia card (High), and it stuttered like a mother fucker, better frame rate sure, but stuttered like a real cunt. 2 months later, the drivers fix it, but its annoying to think Nvidia had this shit locked down ages ago and only now ATI are up to speed. GTA4 also always ran terribly, whereas my 8800GTS 512 ran it absolutely smooth as butter, doesnt make any sense.
If ATI get there drivers upto speed, then they would rock my world, but Nvidia just seem way ahead from my experiences (although atm im having a real fucking problem with there drivers after v182.50, Crysis, Warhead and Wars will all crash at some random point for some unknown reason).