If you think it's possible that your city is getting LTE in the next 2 years, I'd get the skyrocket. It's the same thing as the GS2, but you will have LTE if it comes to your area. If LTE isn't coming any time soon or you think you can deal without it, then you probably could save a few bucks and get the non-LTE version.
Oh, and I would most definitely wouldn't switch to VZW from AT&T. I believe VZW is more expensive and you wouldn't get unlimited data. The GNex is supposed to be coming to other carriers, so if you're heart set on it, it'll come. But I think the SGS2 would be more than enough to tide you over until your contract ends.