When purchasing a new mobile device, for value and flexibility, it is best to not lock yourself into any carrier contracts, which typically last 2 years. There have been some good deals on a few contracts in the past to offset this advice, but not recently. With discount MVNOs getting more aggressive in pricing of service plans, it is a better call to buy your unlocked cell phone directly from the manufacturer, such as Samsung, Apple, Motorola, etc. (or at a big box store) and only then pick your MVNO or carrier to deliver your cellular connection.
For maximum flexibility, in case you have to move geographically in the future and the coverage might change with your new physical location, I suggest you get a phone that has both CDMA and GSM radios in it. For that reason, I have been purchasing phones targeted at Verizon while being able to choose GSM carriers and MVNOs as well.
Keep in mind, if you travel internationally, you will find that you will be mostly using GSM. You are covered both ways with this strategy.