Most of the deals for purchasing the phone itself are pretty much the same. All of the carriers offer payment plans. Though Verizon and AT&T still offer two-year contracts if you want to buy subsidized and don't mind being stuck on a contract. The bad news it that the monthly plans will be higher if you go on-contract, so you're not really saving anything in the long run.
So the deals boil down to what the plans are that are offered. If T-Mobile covers your area well, which you should definitely check beforehand, then they offer the best deal: 3GB per line, 2 lines, for $90 a month if the phones re bought up front full price. AT&T can get you the same price if you buy your phones out of contract outright, but you have to share 3GB between two lines (going up to the next highest plan at 6GB of shared data, raises the price by $30). And Verizon will give you 4GB to share for 2 lines for $120 per month, also if you buy outright.