I've looked at a lot of places all over the place, like Sanctuarys hole and had no luck, except for two Goliaths. I am a level 18 assassin, mainly use snipers, shotguns, and revolvers on occasion I use SMGs.
Loot Goliaths are just rare forms of the standard Goliaths, so the best place to farm them is wherever you find Goliaths. Tundra Express has several large bandit encampments, and I tend to find them and the slot machine Goliaths regularly on this particular map. (In fact, I found one just last night right outside Tiny Tina's...)
Since they're rare, you're not going to see them often. I don't think they're particularly good for farming loot compared to other methods, given their rarity.
Farming a God-Liath requires that you have a somewhat powerful Goliath, and enough enemies to level him completely up.
Good spots to farm these guys balance three factors:
- If the Goliath is too weak, he'll lose to the enemies
- If there aren't enough enemy spawns, he won't level up enough
- If he's too tough, you won't be able to kill him after he maxes out
Again, there are a lot of bandits in Tundra Express. I don't like Frostburn Canyon for this because the flamethrower nomads tend to make short work of Goliaths. When I did this for the achievement, I did it twice in Eridium Blight. There's a fairly large encampment of bandits up on the hill near Grandma's House.
From comments at the Reddit - /r/Borderlands post, "No... DON'T kill the Goliaths!!" (I added the links to the Borderlands wiki):
...I ran into a Loot Goon Goliath at the start of Hunting the Firehawk. I kited him all the way around Frostburn Canyon, all the way up to the entrance to her lair, letting him kill anything that got in our way.
...Frostburn Canyon is a great place for kiting them around to level them up. I always get a God-liath going and let him kill Scorch for me.
The best time to make a GOD-liath is the Slab initiation. He literally did all the work. Also, in True Vault Hunter, I did a showdown to see who will become the toughest Goliath.
I love the Once and Future Slab mission. I just pop the tops off all the Goliath's then grab some popcorn and settle in for some mayhem.