I'd only recommend a nvidia card if you plan on getting a gtx 6xx series card. You can get much better performance out of the SAPPHIRE 11188-22-20G Radeon HD 6950 in comparison to a lower end nvidia card.
Yup, if you have the extra $50 to throw in the build, get the 7850. It's a newer card, consumes less power, and performs on par with the 6970. You can also overclock the hell outta that card more so than the 6950.