Never buy something because of its manufacturer unless its a PSU, thats the rule when overclocking a computer
I voted ATI but I like Nvidia also.
I prefer ATI. I had a Nvidia in my first PC and was very happy with it and then when I got my second PC I got an ATI in it and it seems to have a lot better performance.
I only roll with Ati. Its the best. I love my 2 6990's
Nvidia was my first so I vote for Nvidia
I personally prefer ATI Radeon as I think the performance is better and they look cooler!
I prefer Nvidia because honestly, ATI drivers are horrible. My drivers for my card were so bugged that for 5 monthes I was unable to watch HD videos full screened, would cause an instant BSOD. Really put me off ATI.
I'm using nvidia atm and it's working well.
nVidia is the best without a doubt. It has the Cuda cores and way more Professional Technologies (think about PhysX).
ATI may get more FP's and are cooler, I still hate them because they are fudged up. They have nothing special to offer.
Overclocking/Flashing my nVidia GPU is also a easy thing with the nVidia Control Panel.
They are all the same.. Just because you have a nVidia doesn't mean that nVidia is the best.
And you can overclock AMD GPUs also with their control panel.
I have a NVIDIA right now and was going to switch to an ATI but the fan was to big on it so I had to stick with my NVIDIA gpu for now.