I made it easy on myself and for my employees. I've got an AC AE - for some reason my Macs will choose the 2.4GHz N network (-29dBm, transmit 300Mbps) over the 5GHz AC network (-59 dBm, transmit 1300Mbps) after rebooting the router 9 times out of 10 and after rebooting a Mac 3 times out of 10 - the 2.4GHz appears to be the strongest "signal", but not fastest by a longshot).
I named my two networks differently - "Fast N" and "Faster AC", and prioritized the AC network in Network Preferences (in the admin account on the Mac). QED, for me.
FWIW, we also have a few 4th-Gen AEs and a couple of 1st-Gen Express units on our network - naming the networks keeps it easy for us to choose the "weaker" but far faster 5GHz networks.