I just picked up the 7970 Vapor-X from newegg when it was 13% off a few days ago, so that was a no-brainer for me. I'm sure you can't go wrong with either one. Someone did correctly point out that the 7970 is a better value for single card performance. You also get 4 games right now! If you may go dual card, either due to a higher res display, or multi-display, SLI seems to be a better choice based on Toms' findings with frame time variances.
I just stepped up from a 5870, and this card is very, very fast. If you run a single 1080p screen like me, I doubt either of us will want for a second card any time soon. Look at the way the PC market has been moving the last several years. It's now tied to the console market and the new generation of consoles are roughly as good as a mid-range PC. I think the chances of games coming out any time soon that don't run very well on one of either card, is very low.
The Vapor-X cooler is very nice. The stock fan profile seems to shoot for temps in the very low 60's, and in my case, it succeeds at 50% or lower fan speed. This is still a bit loud under full load, but I don't notice that much when I'm gaming. At idle it cannot be heard over the rest of my system, which is not loud.
Mine is rock solid at 1200mhz and counting even on stock voltage too, FWIW.