When having the same SSID, which band the client connects to depends on the client, not the router. Some wireless adapters let you chose which band to use in priority (my Centrino 6320 does). Personally I recommend using two different SSID so you can fully control on which band you are connecting at any time.
Thanks Merlin, I tried as you suggested but still confused. I have a galaxy note 2 and have set up two Wi-Fi profiles. One for 2.4 & other 5ghz. Due to my house and location of router I have to have 2.4 GHz to reach other side of house on second floor. Problem is when I leave and come back home it connects to 2.4ghz instead of 5ghz even though the 5ghz is stronger signal on main level where router is.
If I try to use 5ghz upstairs on opposite side of house from router. It us connected with a "strong" signal, only 13mbps but, no internet traffic can be passed.
I understand 5ghz doesn't travel as far. But I would think it would connect to 5ghz first. Who knows?