Easiest/Quickest Normal (not pure faction) delve?

I'm finally reaching the end of my delves, with only 5 left to complete level 500 pure faction. So, even the old farm delve (City of Thieves) is now at level 500. Which do you all think is the easiest one to farm at level 500 (normal, not pure faction)? Assume I have all the normal mythics and troops that one could want.

I still need one to farm for shards on days I'm feeling stuck while leveling the hoards up some more, or just not into paying a lot of attention to a delve.