Bang for the Buck
Value always matters. Most of use have limited cash that can be used to indulge our gaming habit, so we naturally want to buy a video card that provides as much bang for the buck as possible.
The Radeon 6950 has an MSRP of $299. As of this writing (Dec 15, 2010), Newegg listed five cards at this price, of which three were in stock. Only one other 6950 was available and in stock, and it was priced at $309.
The Radeon 6970 has an MSRP of $369. As of this writing, Newegg listed four cards at this price, of which three were in stock. Two other cards were available for $379.
The Nvidia GTX 570 is at $349, and the GTX 580 is at a whopping $509. Given these prices, the Radeon 6950 is the clear winner. It offers performance about the same as the GTX 570 for $50 less. The Radeon 6970 is competitive with the GTX 570, as it is quicker in many benchmarks, but only slightly so. The slightly more expensive price therefor seems appropriate. The GTX 580 clearly loses any value argument.
Keep in mind that prices can change at any moment, so please double-check before buying.