The different 802.11 versions are indicated by the letters afterwards. They indicate the maximum throughput speed for the device. The most current one is ac. I would recommend buying ac or n, which is the version prior to ac. All of the versions are backward compatible and will allowed older devices to be used at their own max speed. So if you have a device that works on 802.11g connecting to a router with 802.11ac, that device will get 802.11g max connection, and at the same time a device with 802.11ac will get the max ac speeds.