[Darth-Apple]

If you plan on upgrading to something better anyway, either is probably a good choice. They are both relatively entry level and would need to be replaced eventually if you want something higher-end. If you don't want to wait, the GT 640 would tie you over. If you want something that will keep you covered for at least a couple years, I'd definitely go for the GTX 650.

Then again, I'm big on future proofing my hardware. I don't get the best tech on the market, but I try to at least be somewhat midrange in my choices.