mainly myself in NVHM and mostly just to see how long a level 29 - 39 toon will survive tier 3 and how much damage it can deal. But yes, it can be used for PL’ing people from 1 to 50, higher then that though is just not feasible due to dwindling XP amounts the higher you go.
Mostly if I power level others, I jump into an OP 8 toon and run the Bar at OP 8
My preferred is whatever gives the most XP the quickest, which for me I believe is the BarRoom, I can clear it in about a minute, averaging about 1 round every 1½ minutes.
best method find someone on PS4 to level you up to your Brothers level
I agree on the drops (he’s very stingy about his drops), but he is a quick kill for XP farming and as VaultHunte101 says “it’s nice to have options and variation”
doing all DLC’s (or most) in NVHM is also an option to catch up to his Level