+1
As a hardware knowledgable person myself (but not the hardware person KnightWRX is suggesting, although I can write X86 assembler code) and someone who has worked in IT for a long time I can tell you that vid cards flip flop quality and features wise. Brand loyalty among vid card manufacturers is stupid.
+1
Both ATI/AMD and nVidia have had good and bad products.
Good being the Radeon 9x00 series, X1xxx series, 4xxx series, 5xxx series and 6xxx series. nVidia having the 8800/9800, GTX 460 1GB and 560 Ti.
Bad ones would be the Radeon 2900 and 3xxx series, nVidia with the 8600m, the 470/480, and the older GeForce 4MX, 5200/5600/6600 series.
When it comes to computing, at the current time, I'll take what's the best performance and/or price/performance. I used to rock an Athlon 64, as they'd run circles around the P4. Now I can't recommend any AMD CPUs. Intel has better performance per clock and better/less power usage, and given that Intel has been at least 1 die process ahead of AMD for the past few years, that's not going to change, unless Bulldozer is actually the next Athlon 64.
Same with GPUs. If Apple offered it, I'd get a GeForce 560Ti/570/580 in my iMac if I could. But a year ago and change, I'd be rocking a Radeon 4870/4890.
It's hard to be loyal to a brand of GPU company, ever since 3dfx showed that you can easily fall from grace almost overnight. Pick the best card you can for the time, and most likely, be ready to switch at any given notice.
I know before, if 2 cards I were looking at from ATI and nVidia were avilable, I'd go with nVidia as the unified driver thing made things a lot simpler. Now it's basically a wash.