i would say that 8800gts would be much better and future proof. i would say that u get 640mb version because future games would require that. but the main use of more memory is when u have to play games on higher resolutions. at what resolutions do u play
Between those two cards, the X1950XT is better. Look here.
The 8800GTS 320MB is currently 90 bucks more than either card. And that's the cheapest one from Leadtek.
I am using the X1950XT on Neverwinter Nights 2 and play it on a 22" 1680x1050 screen. I can play the game with most of the eye-candy turned on.
If you are on a budget, the best thing for you to get is the X1950XT and an extra gig of ram which is cheaper than 1 8800GTS. Only get the 8800GTS if you already have VISTA. If not, than the 8800GTS will be pointless as you won't be able to run DX10 games with DX10 turned on anyway.
Look at the description under warranty on Newegg. Sapphire's warranty on that card is 2 years parts and labor. I think in the USA Sapphire contracted out their RMA procedure to an independent company. I have not had to try it. But it is first covered by Newegg's standard policy of 30 day refund and 1 year replacement. Newegg rocks that way as I have had them give me my full money back on a 10-11 month old card that was no longer in stock nor worth as much.