I have ATT on an iPad1, but went with Verizon for the "New iPad" since they have full 4G coverage in a nearby city, where ATT does not. I spend a lot of time there.
I need the hotspot for my MBP and ipod. 5GB/month for $50 with tethering doesn't sound too bad, but they'll probably stick another $10 charge on top.
NYC just got LTE on AT&T. I was tempted to get the Verizon version, but I'm not yet sure how often I'll use the data feature, and like the flexibility of dropping into the 250MB plan that AT&T offers. Plus, LTE is on a different frequency from 3G for AT&T, so it gives me a chance to see whether I should stick with AT&T when I get the LTE iPhone (5?) later this year, or consider making the switch to Verizon. AT&T's 3G is worthless in NYC (even if 5.1 makes my iPhone report it as "4G"). If LTE is the same way, then I'll return the iPad and get the Verizon one. It's the capacity, not the coverage, with AT&T. I get 4 bars of 3G in my office, but between 9:00-6:00 little goes through.