64GB iPhone 5, 32GB iPhone 5s, or 16GB iPhone 5s?

Hey guys,

So I'm planning on jumping ship from Android to iOS sometime in the coming month, but I'm just not sure which device to go with. I'd like to go no-contract (I'm in the US btw) and my budget is $650, so here are my options:

1) Buy an unlocked iPhone 5s at $650 and use it on T-Mobile's $30 Monthly 4G plan. My current phone (an HTC One S) is on this plan, and coverage is good, so I'm not worried about that aspect. Alternatively, if I ever wanted to get more minutes, I could pretty easily switch over to Straight Talk. This choice would also give me the ability to sell the iPhone later on, unlocked, which should fetch a decent amount of money, allowing me to upgrade easier when the next iPhone comes out.

2) Buy a 32GB iPhone 5s on Virgin Mobile w/ the $30/month plan, which would also give me 200 more minutes over the T-Mobile deal. However, while Sprint has decent coverage for me, I'm not so sure about data speeds, and I haven't heard too many good things in that regard. Another thing to consider with Virgin Mobile is that the iPhone is locked to their network, meaning resale value will likely plummet.

3) My last option is similar to #2, but with a 64GB iPhone 5. All of that storage is tempting, but I'm not so sure I want to get a year-old phone.

Given all this, I'd like your help in deciding what storage size/model to get, and any opinions on carriers. My current One S has 12GB of actual storage space, and thats filled all the way up, so I'm wary about going with a 16GB iPhone. On the other hand, I would very much prefer not to go over my budget as I am a college student with limited funds.

So what's your opinion? Help me figure this out!