Diablo

I’ve read that farming stuff 3 lvls above you is the most efficient way to farm stuff like dungeons. But might want to watch a yt video to confirm that. Anyway. That would give you 30% more experience (10% per lvl above you) without it being too difficult and spending too much time clearing.

So a good rule of thumb for which lvl nightmare dungeon you should try is your character level minus 50. That would put you at a nightmare dungeon where you are facing mobs +3 lvls higher.