We would need to know much more to even begin to answer that question. What is your monitor's resolution? Do you want to switch to 3 monitor gaming any time in the foreseeable future? How much do you have to spend? What kind of processor do you have? What is the brand/model of your power supply? Does your case have good air flow?
In general they are both good deals for the money. Only you can decide whether the extra money is worth the extra performance for you personally. Unless your resolution is over 1920x1200 the best choice is probably to just save some money and get a single GTX 470 and overclock it. Anything more is just overkill really.
if sli, 460 should be good enough. if you like best performance and don't care cost or even consider triple way, go get 470. when you select 470, remember don't pick reference card like. somehow nvidia don't know how to make reference card. new gigabyte 470 is what I recommended.