I was debating between Shiva and Cthulhu for the Mtix and eventually went with Shiva. But I actually just got Cthulhu off a random gacha ticket

So now for water himes I have:
Vohu, Ryu-oh, Aphrodite, Snow Raphael, Shiva, Cthulhu.
When unlocking 4th/5th accessory slots, who should I prioritize? I'm not too sure which himes would end up being core members in the long-term. On a similar note, what are the best water comps to go for?