I won't purchase any Android phones on contact. I despise carrier bloat and restrictions and the only way to limit this is to buy unlocked versions off contact. I've owned 4 Android devices and only one was a carrier version--a Galaxy Note II, and I immediately had to root and flash a custom ROM to make it tolerable. While I've rooted and played with various ROMs on many of my devices, I'd must rather be able to use a device in its stock condition. Needless to say my time with the Note II lasted about a month.
Only phone I'll buy on contract is an iPhone as they have no carrier bloat, I'm not handcuffed by the carrier when it comes to updates, and I can flip them for a much higher return. Any Android device I get with be unlocked.
After all that, if I was to pick up an Android phone right now, it would be a Dev edition Moto X or Nexus 5, off contract and unlocked, of course.
I'm a T-Mobile customer and have found very little T-Mobile Bloatware on their Android devices. Samsung and HTC pre-installed bloatware is another issue.
T-Mobile's new "un-carrier" and JUMP plans have made it too easy for scammers to sell phones and then claim them as stolen after the fact. There's almost nothing you can do to protect yourself except for buying a new device so that's why I'm leary about buying a used phone.