Out of those two I personally would go with the 5970, but that's mainly because I feel the GTX480 was a poor design and won't touch them so I am very biased.
However, with the release of the GTX460, I personally would hang on for a while to see what else Nvidia has planned, I would expect a newer version of the GTX470 or 480 to be coming out which would be a much better designed card (like the 460 was compared to a 465) and probably more powerful