There's a lot of variables. Certain places in zOMG give higher amounts of gold, there's loot boosters such as a gold potion or Fortune's favor ring, amount of decent booty-grabbing threads/tanks, gold nerfing, and so on. Do a little experiment and see which you prefer doing. Personally I find myself making more gold with BootyGrab than with zOMG. But zOMG can be more fun and worth the time spent.