If I had to purchase an Nvidia product, I would get the 470. Sure it may be slower in most titles, but it has more features and runs today's games at a reasonable frame rate. Also if you have never used dual GPU personally I would suggest staying away from it. Many titles will not use your second GPU, or will not use it correctly. If you view the graphs from FRAPS and HardOCP many games still have near the same minimum frame rate only jumping a few frames, and lastly some people notice the dreaded microstutter.
I would, and did, purchase an ATi product this round. I hope they are able to do a good respin of Fermi and come up with a more reasonable price tag for next round.