From the start, as areas become available!
Frostburn Canyon - several spots, and lots of weak enemies to level up on
The Dust - Buzzard Achademy, Moonshiners shack and Bug Gulch
Tundra Express - Best method is to pop helmet, and let him chase you. Lead him out of the bandit camp, and level up on varkids. Bandits will usually kill them.
Sanctuary Hole - Bandits will usually kill them here, but… sometimes it works.
Thousand Cuts - A lone Goliath spawns above the stairs that lead down to Terra. Lure him across the bridge towards the next area.
Thousand Cuts (again) - At Brick’s place. Pop the Helmet on the BA Goliath to the right. He will usually jump down and go to work. Sometimes he beats up the other BA Goliath, who is passive. Kill the BA Marauders that spawn in, or they will usually kill him. If done right, he will reach GOD-liath before the other Goliaths spawn. Kill him, and pop the helmet on the 2nd BA Goliath /if he’s alive) that’s still standing beside Brick. Otherwise, just pop helmet on one of the others.
Thousand Cuts (yet again) - During “Defend the Slab tower” you have excellent opportunities to level them up on all the loaders. Fail the mission if you wanna repeat the farm!
Eridium Blight - Leveling up or bandits killing them is about 50/50 here. Best spot is the camp near “Lover’s Leap”
Sawtooth Cauldron - Lots of them here, but also lots of tough enemies. Can be tricky!
There’s also the Bandit Slaughterdome…
The best chances for success are in Frostburn Canyon, The Dust (Bug Gulch), Tundra Express and Thousand Cuts. You’ll need to take down most of the bandits, or at least widdle them down to really low health. Kill any enemy that can be a potential threat to your “pet”!
One of the best things about doing this is the hilarious dialogue you get from both goliaths and bandits. I love doing it!