Both cards would run current technology at medium levels. If that's what you want then either is fine. Now for a little more you should be able to get a 6600GT which is better then both of those.
However if you are looking at a card that will perform well and keep performing well into the future then you should be looking to spend at least $250 on a video card.
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However if you are looking at a card that will perform well and keep performing well into the future then you should be looking to spend at least $250 on a video card.