Nvidia, hands-down. I've owned both ATI and Nvidia cards. Here's what I got:
Nvidia cards give you more bang for buck
-Nvidia cards out-perform their similarly priced ATI competition (for example, my 7600GT destroyed my X1600XT in the benchmarks).
Nvidia cards have better cooling
-ATI cards have flimsy, noisy fan-sinks and seem to overheat faster.
-Nvidia cards have an overclocking advantage because of this.
Nvidia cards are more reliable
-Most Nvidia cards offer lifetime warranties, some even cover overclocking
-Two of my ATI cards failed within a year of purchase, while none of my Nvidia cards have failed yet.
Nvidia has better drivers
-ATI Catalyst Control Center has always given me problems with applications, such as Maya.
-Nvidia drivers are typically more stable, while I had frequent crashes with ATI.
-Nvidia drivers are released more often every time a major game is released to offer improved compatibility and performance.
Nvidia cards have better game support
-A higher percentage of games have the Nvidia logo on the back and perform better under Nvidia cards.
-Nvidia has superior OpenGL performance for games like Doom 3 and Prey.
Nvidia is ahead of ATI overall
-ATI released their DX10 cards much later, and they were left in the dust by the new Nvidia cards (and ATI kind of copied Nvidia's unified shader technology and claimed it as their own).
Nvidia does better in the rendering area
-Nvidia Quattro is the choice for large developers, whereas FireGL cards aren't very popular.
Nvidia chipsets are a first choice
-ATI chipsets are declining, featuring none of the benefits the Nvidia chipsets offer.
-Nvidia offers options for motherboard and chipset overclocking/tweaking from within the OS environment.
SLI>Crossfire
-SLI motherboards are offered that allow full speed for both slots
-No cable between cards
-Wider compatibility and support
i woot for Nvidia
i had a ATI once, it screwed up in 2 weeks, so i got another, it also screwed up so i went back to NVidia
i also like SLi more than Crossfire. I also dont like AMD much so now ATI is AMD....
NVidia all the way.
the strongest ATI is not as powerful as the strogest Nvidia card.
the strongest ATI card need a nuclear power supply :S.
NVidia rules.
addicted to "8800 series"
Ati, there newest cards are the best bang for the buck on the market. Plus i have had both and while Ati may be behind most of the time, there drivers are usually more refined. Nvidia may have been the first to come out with DX10 but it sucked for the first couple of months, i help moderate a Vista forum and we had all kinds of issues. plus Ati is the first to have DX10.1 cards if we need to go with who was first on the market for DX... Plus in real world usage, how many ppl are really buying high end cards? Most ppl only get the mid range and right now Ati is the best bang for the $$$.
nVidia For the world! I'll go for one of those cards anytime. ATi, not the best cards, but they have been catching up pretty quick to nVidia. Now Intel's on-board chips have to be improved drastically