A longer run for sure, but it would be interesting to try and route the quickest way to level up in the game. I have a feeling it would be fastest in 4 player co-op, so maybe separate catagories for multiplayer and solo.

I think there was an XP glitch, but I don't know if it still exists. Probably should ban any glitch that makes this a trivial category.

Lots of ways to farm exp in Act 3, quick combat ones would be to have some sort of vulnerability on an enemy like piercing from aura of murder armor or orin's dagger. Followed up with fighters spamming many arrows.

Throwing people off ledges and jumping on essentially everything to kill them.

Exploration exp seems to be scaled to your level so might want to delay those as much as possible.

These aren't necessarily glitches but part of the game system. There are some glitches like Raphael being idle and you can freely attack him in Act 1, it takes a while to deal damage normally but if you can get to Huge or Gargantuan size you can stomp on him a bunch of times for "quick" 1.4k exp.

This can get tedious solo, group of 2-4 can make this a lot more interesting.