I'd recommend using the carrier that gives you the best coverage in all the places you need coverage. Price is secondary. Free phone service that doesn't work where you need isn't as good as expensive service that does..
Always choose by carrier by coverage first. (Actual coverage by using a phone there, not by their make-believe maps.) Then choose the phone, again based on coverage first, then by features. (The cheapest "give-away" phone isn't going to get you the same coverage, on the same carrier, as the flagship phone.)
Choosing a phone first, or choosing by price (or by anything but coverage) is like deciding on which car to buy based on which one comes in the color you like. And since we don't know who has what coverage where you are, we can't give you a sensible answer. (You can even choose by technology first or second - a weak CDMA signal actually makes some people sea sick, while a weak GSM signal makes some people dizzy. They sound completely different - underwater vs way overdone autotuning.)