We also get Hercules with her first set of buffs (lowered cooldowns by 1 turn/raise duration of buffs by 1 turn).

Slimee:
If you're the type to stick with 2 teams, then I'm thinking of SSR Nike, with Water/Wind being your main two. Ryuu-Oh is another good pick if you're not bothered by her rendering Cthulhu's A-frame atk debuff obsolete.

But if you're the type to constantly change teams for elemental advantage, then don't pick a water kamihime. Unless we get a rerun of a reprint that we've already gotten, we're not gonna see Fire for another... 17 or 18 events? Somewhere in that area.
Sol and Amaterasu are safe utility picks to raise the floor of your other teams. I'm not sure if they're necessarily optimal, but they will never be bad picks.
Probably don't want to pick a different Light kamihime. Aside from Sol being the most useful one, I only expect 1 Dark event for us in the next 5-6 months. Fire will see more use, as there's... about 4 times we'll see Wind in the next 6 months. 1 advent, 1 raid, 1 reprint of that 1 advent, 1 union.
But if you stick with using Mordred, then Sol looks better.
We'll also see Thunder about 4 times in the next 6 months; 1 union, 1 reprint of that union, 1 reprint of Mastema advent, and 1 raid. But we don't yet have the awesome wind SSRs.
For Water, we'll see a raid (next event!), union, raid, Vritra reprint, and a new advent in the next 6 months or so. I have my doubts that spending the miracle ticket on Tyr or Raijin/Raikou/whatever is worth it.