Thats really difficult to answer in such a generalized way, since it depends on a ton of different variables including your skill edge in various games. But assuming, that you are a winning player, then games with deep stacks, slow blinds and large fields will have the highest ceiling on ROI (Return on Investment), so in general large field regular speed MTTs.
This is only half the story though, since these games also take more time on average. So while your ROI might be high, your hourly winrate might not. There is no solution to this other than to simply try different games and see, how it goes, and just as importantly if you like them or not. Some people for instance hate the way, microstakes PKOs play, and then they should not play those games, even though they might be very profitable for people, who enjoy them and adjust well.