What I found interesting is if you kill one of the 3 rakkRakk flying around in vault of the warrior one will continuously spawn from a spot around the arena flying at you and attempting to attack you. This
This becomes quite awesome because they do not stop coming at you, if you're prepared to stand on the spot (at the bottom of the stairs just before you fall into the arena is the best) for a while, it's good xp. At
At level 50 playing TVHM they give you an average of 300xp300 XP per kill. If you have adequate power in your shots or a good gun with a decent size mag they will drop like a rock. If you have the bee one hit or if not maybe from 2-3 or 5-7 depending on power of gun. This becomes around 3000 to 6000 xp if you can kill 10-20 rakks, in one magazine. So after only 4 mags you get the same xp as if you killed the warrior.. This
This is great for boosting another character, just throw him in your game and kill rakk with your lv 50 guy and xp is yours. It is a bit time consuming but not as much as other methods, and it's damn easy. Hope About 20 minutes to get lv 47 commando to lv 48.
Hope this helps :)