Your router has a Internet port monitor which might give you an indication of the traffic on the different radios.
My router has a Network Traffic Monitor where I can watch the traffic on either of the radios. Something you may want to try, say for testing, is put the two radios on different SSIDs. You could then connect to whichever radio you wanted to test by connecting to that SSID and looking at the receivers for signal strength and traffic.
One radio may be better for some things, and the other more useful for others. If you were in a busy area, it might be advantageous to use the 5 GHz radio since it may not be as busy as the other one.
I found my 2.4 GHz seemed to have a stronger signal, but was susceptible to things like...