well, if it's not possible to farm higher, than i agree with shellshock. otherwise i would strongly recommend circle of fire
reasons:
1. you earn more than 4400 gold, thats pretty nice
2. you level up faster, because killing more and higher leveld enemies is speeding up the progress bar
3. more powerful items drop, which can be sold in the shop
i think it's the best level to farm, but it's hard to beat it on auto, i can make it about 85% of the time with 2 5* chracters with maxes talismans.
you can beat it with only 4* chars manually but the dumb automode makes it a lot more difficult