Truly depends where you'll be spending most of your contract time and who gives the best service in that area.
It also may depend on service features you may desire. For instance, if you feel tethering should be included in your data plan, then Verizon may be the way to go but if that isn't a deal-breaker, then your golden unlimited plan may be the way to go.
But that speed and service..that's the kicker to all of this. If all of the features you have can't be enjoyable where you are or may end up going, why hold on to it, it has no value at that point to you.
I'm here in the DC area (Alexandria, VA) at the moment and just bought my fiancé her SG3 on Verizon. They have really nice features on their plans but I wanted to see speeds with Verizon vs my AT&T. While she was getting between 12-13Mbps, I was getting 22, and this was inside their store!
So it truly depends on what features you need, who is providing them in a way that is benefit to you.