Cozmooo
honestly the best worlds I can think of for MC and Rivera would be "Fate and Fairy Tail" although it's worth remembering that in these 2 worlds the level (power) is much higher than in danmachi, of course fate if you choose the anime is even fair enough with danmachi, but Fairy Tail the anime is simply much stronger than danmachi. As for why these 2 worlds? honestly, MC would love the geniuses there and for Riveria it would be paradise, after all the amount of magic in both worlds is surreal. other interesting worlds: DXD, Genshin impact, Mahouka koukou no rettousei,