From which American operator to take iphone 6s?

Question

Online shopping

I decided to try to take the iphone 6s from the American store. In the store, you need to select one of the operators, despite the fact that the full cost will be paid and the phone will not be locked. Nevertheless, which operator should I choose so that the handset is compatible with our gsm providers (I do not have and will not have 4g)?
at&t, sprint, t-mobile, verizon?

Answer 1

6S so far on the Apple website only locked. Look at 6, there is a Sim Free option .