Yesterday, Google announced their latest Nexus phones. If you're unfamiliar with the Nexus line, these are the phones that get the full blessing of Google. This means that they will not have anything extra installed by the phone manufacturer nor will they have a customized version of the Android software. These phones are released to function as designed by the Android team.
They give you the freedom to select any carrier you want, switch whenever you want, and get the latest software updates when available. All of these benefits and they will cost you several hundred dollars less than a Samsung Galaxy S6.