They are slightly different models, though both are unlocked to support any carrier's SIM cards. The T-Mobile version will come with a T-Mobile SIM card, while using the unlocked version with tmobile will require an extra trip to a tmobile store to get the appropriate SIM.

They each support different LTE bands. The unlocked version will work with LTE in most European countries, while the tmobile version will work with LTE more in Latin america. Both will work with 3G just fine everywhere.