The two are very close in performance. What mobo do you have? Is future Crossfire or SLI a possibility? If you care about PhysX, the GTX550Ti is your choice. If you will engage in bitcoin mining, ATi is the way to go. Check the benchmarks of the specific games you [want to] play. Blizzard games and Civilization strongly favor nVidia, but Dragon Age 2 doesn't get along with nVidia's drivers at highest settings (ref. HardOCP).
Really? Hmm, I guess. But to me the most appealing aspect is the life time warranty. Um, sorry if I seem fickle, but another card has peaked my interest. The 6790. Its in my price range, and it has a life time warranty. http://www.newegg.com/Product/Product.aspx?Item=N82E168.... And my mobo, Its a budget one, 50 dollar range. I dunno the exact type though. But how does that card stack up to those two?
Its worth pointing out to make sure people have a decent enough PSU to power a card that uses 2 x 6 pin PCIE cables but that dosent make the card bad value.
Its the power usage that jtt283 is referring to which may matter to some but really should not come into the calculation when comparing value/performance.
A 6790 is noticeably, game changeability faster and about $10-20 dearer. Personally i can live with a ratio like that. I wouldn't recommend the card myself as i think the 6850 is the best balance of price/ perf at the moment, with the cheap 5850's having seeming to have disappeared.
Oh right, I'll be playing WoW, Gta IV, dragon age 2, and I kinda wanna start playing at 1080i resolution...
WoW prefers nVidia cards, but Dragon Age 2 has driver issues with nVidia at the highest settings. Still, WoW is playable at decent settings on ATi cards too.
If you want more power than a HD6770, getting a HD6850 makes a lot more sense than the HD6790. It is more powerful, and uses less power. The small price difference is worthwhile.