I wish AT&T could get their crap together, they started rolling out 4g but I cant even get 3g working in most places, go figure!
unfortunately, Metro PCS is horrible where I live. it's probably the worst.
I personally use Tmobile and it works great where I go, also I think only ATT has no unlimited plan. everywhere else, at least to my knowledge has Unlimited and 4g or HSPA+
I can just see it now, LTE 4G iPad next year.
(I know, but I can still dream about it)