JManM
Honestly, just from power level I would say the best option would be star wars followed by dragonball. He currently doesn't have the power to survive even the weakest saiyajin even with armor and weapons. Force shenanigans would be a good bridge to give him way more survivalbility. Also does he really have to eat them? Both characters aren't evil, one is naive and emotional the other just a harmless perv. Force ain't that hard to unlock since he will be filled by it upon ariving in the star wars universe. And something all fanfics can agree on, is that random energy suddenly existing inside xou ain't that hard to sense when you never had it before. As for Oolong, it was stated by the ccat uddy from Yamcha that Oolong never fully l arned his unique transformation magic, since he dropped out. Which is why he can't make himself stronger for example. So in both cases eating them would be a waste of a character and inefficient (And if someone can make both characters way better it's some good old Grunt teaching)
I can’t decide all of them sound so amazing one is witcher meets dragon age which sounds very interesting two he goes to Star Wars and becomes force sensitive just the thought of a force sensitive grunt going through Star Wars and making it his play ground is amazing and three where he goes to dragon ball and is not only bulma’s perfect lizard boyfriend but he’s in dragon ball that already sounds amazing all of these are just to great