If you're planning on overclocking, avoid a video card that is superclocked already.
If you're not going to overclock the video card, then whatever the given speed is... I assume higher is better.

I went with an eVGA 670, 4GB Superclocked.
From a bang for the buck point of view, this is one of the better cards out there.
A 680 would be superior, but a 670 is still a great card especially if its an interim card until the next thing comes out.