I'm getting a new computer and I have a choice between the ATI X600 (nonPRO) and the GeForce 6600 (nonGT). They both come in 128 and 256 mb flavors. Just wondering which I should get. I was leaning towards the GeForce 6600 as it is cheaper, but does that mean its worse?? Any reply would be appreciated. Thanks.

The 6600 is the better card (see benchmarks). The scores their are going to be slightly higher than real world because of the 600MHz memory speed; real ones run at either 500 or 550. I dont think you would see much if any difference performance wise between 128MB and 256MB.