Need advice for selling iphone 5 and getting iphone 6 plus?

I have a 16 gb unlocked iphone 5 that runs on tmobile right now. I was wondering what's the best option for me. I think I want verizon because I'm joining the Air Force soon and I need good coverage. They have a plan where they take your old phone and give you iphone 6 for free if you renew 2 year contract but I'm not sure if it works for new customers. They have a edge program that looks really good it's $50 a month for 2gb of data?! I was thinking should I wait or is this a good opportunity for an upgrade?

I would trade it in just because its easier, you might get more selling it on your own but time is also worth something. Be sure to wipe it first either way. I think with iphone I would always trade in an upgrade after 2 years because they hold their value so well, that upgrades basically are free for iphone users as long as you commit to a new 2 year contract which is what I do.