AMD as far as we know, make their CPU's compatible with previous motherboards, so for future upgrades they can be good. Intel however brings out a new chipset with each gen. Which, as annoying as it is, they seem to work better together then AMD.
The best way to future proof, i believe, is to build a system that wont need to be upgraded anytime soon, and with Z68 mobo as bill stated is probably the best option. If you did want to go AMD, i personally would wait for Bulldozer.
If the rig is for gaming, 4 cores is ample with most games never using more than 3 cores.