Definitely the E6600. The E6700 is a rip-off, it's nearly $300 dollars more, yet only offers about 10-15% better performance than the 6600, which can probably be overclocked past 6700 speeds with stock-cooling.
Regarding the FX-60: I like AMD better personally, but Intel pwned their ass with the Core 2 Duo, and the FX-60 doesn't compare even to the 6600.
It's very clear the E6700 is the best however, Overclocking the E6600 to match a E6700 would be a breeze. I do not own a core2 duo but i hear they are VERY over clocker friendly.
Id like to note that you would not need to Overclock the card for a while considering a 6600 is powerful enough for anything you can throw at it.