Love_dem_fanfix
All three are nice settings but i would prefer DxD simply because fitting pokemons into Marvel or DC just feels strange. In DxD we have a ton of races and magical beasts and having inteeligent familiars are pretty basic too so it wouldn't be out of place that much. Also the divine cigarette effect which grants him a huge boost to any power systems the world has would be much more interesting in DxD as they have stuff like devils power of imagination based demonic power or the holy stuff from the angels which also lets you wield holy swords, divinity of the gods, Senjutsu, Touki, etc. Meanwhile DC and Marvel also has multiple systems but they tend to be some sort genetic ones or borrowing power from higher beings which i don't think suits the mc that much.