i recon the leadtek 6600GT is the best. that or the EVGA but either way, with both of them at the top, it would be something like this:
Asus/Aopen (actually a very nice card)
MSI
Gigabyte i think.. i could be wrong.
the good thing about a leadtek or EVGA is that they generally better quality cards, giving you more FPS at stock settings, and the ability to overclock further than their cheaper 'competitors'.