1366, 1156, or AM3: which socket has better staying power?

Title says it all. It's time for me to build a new machine, and what I want is a good gaming machine which will run smoothly at 1900 x 1200 (I foresee using this as my gaming display: 46" HDTV, 1080p, 120 Hz Refresh Rate).

Like everyone else I want the best bang for my buck, but I can afford to dump some money into this rig. I want a system with enough power to last 2 years and still deliver 30+ FPS after that span, but then also still be upgradeable in 2 years time so I can just drop a new processor and GPU in it and be done. I don't foresee needing to use multiple GPUs, one good GPU (like a 5850) should be plenty.

With this criteria in mind, which socket will be the best choice for me?

My budget is $800-$1200. AMD is definitely a solid choice, and usually gives better bang-for-the-buck when you price out the entire system. My question though is more to do with the socket longevity. In that regard, AMD has (historically) proven to get more lifespan out of its sockets; however, the i5 & i7 performance is just undeniably better, and MAY translate into lasting longer and having better staying power into the future.

So thanks for the offer to price out a whole system, but really I don't want to waste everyone's time. I'm not asking you to do that for me. I'm just looking for opinions on which socket (and CPU) will have the best staying power, which includes considering the possibility of an upgrade later.