Gundato: Now we are getting OpenCL (maybe). Take a look at OpenCL. It could EASILY stand for "Open CUDA Language"
So nVidia has the head start. Maybe ATI/AMD can catch up, but that is a pretty good head start. Give it a few years and they'll probably be even again, but until then, nVidia has the advantage.
Delixe: It stands for Open Computing Language and is only similar to CUDA. OpenCL is actually more powerful as it allows programmers to use individual CPU cores and GPU stream processors. Nvidia may have an advantage here in that they were the first in opening their GPU's to non-graphics applications but the downside is it's only compatible with Nvidia, which annoyed Intel enough to develop Larabee. Bear in mind that while Nvidia has PhysX ATI will have Havok acceleration which will also be supported by Larabee. PhysX could well find itself phased out over the next few years simply because Havoc works with both ATI and Nvidia, PhysX only works with Nvidia.
For gamers however PhysX offers very little in actual benefit and CUDA is only useful for folding. Again it does not justify the difference in cost between a 5870 and GTX480.
The 5870 also uses less power for the same gaming performance as the GTX480, and therefore runs cooler and quieter. This is primarily because NVidia dedicated way too much of their hardware towards non-graphics applications of the card. NVidia has a couple of large power hungry cards on the high end of the DirectX 11 market, but ATI has DirectX 11 in their entire product line from top to bottom. They also have a better design process for their chips, because of being affiliated with AMD. The reason NVidia was so late to market in this generation is because they got their chip design wrong and had to do a second run before they could release. (There's a detailed article on this at Anandtech if you care to look.)
Things tend to flip flop between the two companies for different generations. NVidia has been on top for some, ATI on others. IMO, the DirectX 11 generation is going to be dominated by ATI because of better chip design and a wider range of products.
CUDA is not relevant as far as I'm concerned. Like you said Delixe, the only practical use for it right now is folding. And all of the major folding apps support ATI also at this point as well. I know someone who is using an ATI 4770 for folding apps and loves it. Other than that, the head start CUDA has gotten will be irrelevant once a standard is established. As often happens in computing, once a standard happens proprietary solutions get pushed out of relevance.
Now, getting off this tangent and going back to the question that was asked...
As far as brands for ATI cards, Sapphire tends to be the cheapest and uses reference designs. So they are a good bet if you are price sensitive. XFX has the best warranties and the best memory chips for overclocking. So if you can get an XFX for a good price, they may be the best way to go. My last two graphics cards have been PowerColor. They are somewhere in the middle between Sapphire and XFX, but are great cards for the price.
