Both AT&T and T-Mobile have coverage maps on their websites. I'd look there and see how it is for your area. If you have good T-Mobile coverage where you live i'd go with them as they have much faster data speeds. If you don't have good T-Mobile coverage you can still go with AT&T.
T-Mobile has a $30 a month pre-paid plan with unlimited data, unlimited texting, and 100 minutes. If you need unlimited minutes you can go through Straight Talk, which offers unlimited everything for $45 a month off contract. You can choose to run through either AT&T or T-Mobile with straight talk so you can still get T-Mobile's speeds with unlimited minutes.
No matter what you choose you should order the Micro SIM (this is important, Micro SIM) card online.