Help me escape Verizon

Thought I would come to the Verge's mobile community and get some advice.

I'm a long-time Verizon customer looking to jump ship when my contract comes up. I'm currently on an iPhone 4S with unlimited data, which Verizon will be taking from me if/when I choose to upgrade to 4G with them. Not only that, but I'm getting tired of this contract nonsense and considering switching to prepaid.

Personally, I don't have a preference between iOS, Android, or Windows Phone. So help me out here. My Verizon iPhone is worthless with any other carrier right?

My limited "contract-free" knowledge tells me my best bet would be to sell my 4S, pick up a Nexus 4 (or whatever the latest Nexus is this fall) because they are relatively cheap, and then sign up with T-Mobile.

What are you thoughts?