What do you want to do? Assuming gaming is the reason, what's your budget? If you're any where in the $200-$300 range, AMD is your best bet, they just announced large price cuts and you can get some very powerful cards cheap. The HD 7850 is about $200, the HD 7870 is $250 and the HD 7950 is $290.
Yeah, no. The GTX 660 Ti is not a great card anyway. The 192bit Memory Bandwidth hurts performance even at 1920x1080. The HD 7870 is slightly faster, and $60 cheaper and the HD 7950 is much faster and $10 cheaper. Why would you even recommend that?
It is extremely easy to remove the old drivers. In fact I do it even if I upgrade from one nVidia card to another. Just uninstall the old drivers like any other program using the Add/Remove Programs tool and then download and run the program "Driver Sweeper" http://phyxion.net/item/driver-sweeper.html .
Then just download and install the latest drivers from AMD. AMD has made up some ground in recent years on nVidia in GPU performance and generally they are neck and neck. I don't really prefer one to the other. My current card is the EVGA GTX 690 because it was such an incredibly engineered and designed card. Before that I had 3 Radeon HD 6970's in TriFire (Really a 6990+ 6970), and they performed great and scaled performance really well. But It was a loud and noisy setup.