Based upon the fact that after the deal closes and we'd all have to get new phones due to the loss of 3G on our current devices and granted you stick around, which phone on AT&T AS OF RIGHT NOW, would you all get?
In that case who really knows what'll be out in a year? Quad core will be for sure. Imagine the display resolutions those chips will be able to drive. Can you say full HD screens on a smartphone? I would LOVE for that to happen.
If I was buying a phone today and could choose from anything from either carrier it would be the LG Thrill. It'll be out this summer. I like the G2X but the thrill is faster (and 3D for what it's worth). If we're going for not waiting than it would be the G2X and when I'm forced to change I would sign a new contract and get a new phone then.
Remember, get what's best for you now. Either way you'll be signing a new contract when you get a new AT&T phone.