This question has been getting a lot of debate recently. Which card is currently king? The benchmarks and comparisons are coming in from all over the show. Toms Hardware has one. As does Benchmark Reviews. As does Gizmodo. As does Maingear Forums. As does Dutch site hardware.info (excuse the google translation). The latter two even have SLI comparisons. (For anyone considering a truly high-end system, the SLI comparisons have to be the ones that matter.)
Unfortunately, the benchmarks are far from conclusive. They all agree that the GTX 480 is the fastest single GPU on the market. Fair enough. The Radeon HD 5970, with 2 GPU's is faster. Also fair enough - so the nVidia chip isn't double the speed of the ATi chip.
The nVidia card does well enough on the synthetics, (although here you see it beaten out by a stock Radeon HD 5870,) but that doesn't really mean anything. In general, the nVidia edges out the Radeon chip, while falling short of the dual ship board on almost every benchmark.
However as soon as you start to run SLI setups, it becomes less clear. The results are all over the place - or are they? Where the reviews fall down, is that they don't put their finger on the important difference between the chips. They will tell you that the nVidia chip doesn't scale well in SLI. They will also tell you that the Radeons actually come out ahead in some of the benchmark comparisons.
I think I see a pattern emerging.
If you look at the more taxing games, at high res and max'ed out detail, like Metro 2033, (you might need to google translate that,) Crysis and STALKER Call of Pripyat, then the nVidia card has a solid edge.
Other, less taxing games, like DiRT 2, Far Cry 2, and HAWX show the Radeons ahead in places. You'll note that in these games the frame rates delivered by either chip are so far into playable territory that you won't really care.
What matters here is that, at the top resolutions and maxed out detail settings of the most demanding games, the nVidia always wins. Basically, this is a chip with a mission. The GTX 480 is here to show you the most beautiful games at their very best. For those games that give it up for just any old GPU, there are the Radeons - but for those of you that want to see something you've never seen before, the GTX 480 in 3-way SLI makes 2560x1600 more playable at max detail in Crysis, STALKER CoP and Metro 2033, than anything else you can buy today.
So, if you want to play these games through and enjoy them, ATi has the cards for you. They are affordable and playable. But, if you want to see what the state of the art looks like in PC games today, nVidia has the only chip that will show you that.
With Crysis 2 on its way this September, I'm guessing there will be some eye candy that will really show off the capabilities of the top-end rigs. I wanna be ready for it.