I'm assuming it's best to use 5Ghz over 2.4Ghz if your device supports it?

Use 5Ghz, think its better...

I've found it totally depends on the circumstance.  Sometimes in some locations, the 2.4 works better.  Some locations the 5 will work fine one time but not the next.  Doesn't seem to be any rhyme or reason to it.  Could be interference from other devices nearby using the same band.