Default T-Mobile Smartphones...what's unlocked, whats NOT

Hey, I'm just another sucker paying Verizon $310+/month for 4 smartphones. I am REALLY tired of it and am just about ready to walk into a T-Mobile store very soon!... Or should I say JUMP? Anyways, I cannot stand the thought of having a smartphone with a locked boot loader. I currently have one of the original Verizon Samsung Galaxy S4's, which is really pretty great for someone like me! And I could give you a list of the best Verizon devices and developers (for an XDA junkie like me), but I couldn't tell you a single thing about development in other carrier's phones.

So, I'm here to ask if you folks on T-Mobile would kindly share any info you have with me on where T-Mobile smartphones stand in the world of rooting, unlocking, romming, flashing and just general Android development. Which T-Mobile smartphones (or even brands) have unlocked boot loaders, and serious development along with them?

Thanks for any feedback!! ... Seriously!
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