It really depends a lot on why I'm farming. I've been playing the game less than half a year myself, so pretty new also.
At the moment, I'm trying to push a char to map lvl 500 to farm around that level, as it yields a higher(the highest possible) level of crystal and rune drops as far as I know.
If you can clear maps around that level with no problems, I believe that is the best floor.
That said, you might be farming epic->legendary->mythic quest to get a guaranteed eternal, OR you might be rushing through maps to kill the enslavers in hope that you get legend/eternal pets.
In those two situations, you're better running through lower map levels, straight to the enslaver/bosses of the map, just because of the speed of the run.
What is the are the intentions behind your farm run? Items, gold, drops or all of it? Let us know, and it might be easier to give you advice:)