For 2.4GHz/5GHz wifi which is best for Apple devices: different SSIDs or same? My WiFi router, a Netgear Nighthawk, can do 2.4GHz and 5GHz; and it can have the same SSID or different for those ranges.

We run MacBooks, an iPad, an iPad Nano and an iPhone 4 on the network. Does it make sense to have both ranges on one SSID and let the devices pick the right frequency or keep them separate?
I have a similar set up (not same router).

While using the same SSID, I noticed instability, probably due to randomness  of who gets what.

So now I have separate SSID for 2.4 and 5 GHz and I decide who connects to what.