I've been using a cell phone for over 18 years now. Never, ever, EVER will I sign another cell phone contract. Ever. Once the ink is dry on that contract, the cell companies can treat you like crap for 22 months because what are you going to do--pay their $400 early termination fee? They don't start being nice until just before your contract is up for renewal, and then they trot out their new phones trying to lure you into another 2 years of slavery....
Would you sign a contract to only buy your gas at Shell for two years?
Would you sign a contract to only buy your food at Safeway for two years?
Would you sign a contract to only buy from Dell Computer for two years?
Of course you wouldn't. So why the hell would anyone in their right mind sign a cell provider contract???
Prepaid is the only way to go, and ever since Boost came on the scene with their unlimited plans so many other carriers have had to follow suit.
I remember 20 years ago when the phone company actually charged for "local long-distance" (calling between two cities in the same state) because they could. Internet telephony has forever changed that landscape and I'd say that within the next 5 years less than 1/2 of cell phone users will be under contract.....
Back to your original question, ahead of price I think is the coverage in your area. You can get a screaming good deal on airtime, but if you're always hovering between one and two bars of coverage, what's the point?