Best variant topic

I am looking at getting a M7 as a media player. I like the unlocked bootloader over the old S4 that I will end up selling. I dont go crazy with custom ROMs but id like a good fast ROM, maybe CM.

Question is, which is the best variant of the device for custom roms. specifically the sprint variant seems to be the cheapest because the lock out ESN often. is there any limitations to the sprint variations that mean i need to spend more?