Medea is a solid first choice 'cos she's very versatile and useful in many situations:
  • She can nuke super hard, allowing her to fight harder battles than Solomon and also super good for tower if you're willing to invest in her weapon for different elements.
  • She can also be configured to debuff - can do both elemental def and atk down, so if you're solo-ing stuff and missing one debuff frame or just want to play as debuff support in a raid, she can do that, too.
  • You can also configure her to have a team-wide skill CD reduction every 8T; pair that with hour of the overlord, you can use that twice every 8T. I leave it to your imagination for the kind of stuff you can pull with that

Depending on your setup, Hector (T4 Sieg) can be good for MVP-racing, too, not just dummies. Remember that Och is a phantom guardian, so it doesn't matter which element you main, the critical will still be useful there. She seems to be largely supplanted by Yori (T4 Shingen) when she comes out though for MVP-racing (although for hardcore MVP-racers that want to remain on the cutting edge, she's still probably a good investment.)

Another one I think ppl should consider is Asclepius (T4 Andro) if you like to AAB. Her base heal cap is beefed up to 2000, so at max ascension that's 6000 raid-wide heal versus 4800 from Andro currently. In addition, you can configure her to auto-revive herself and one ally once every 12T, which is a nice insurance. Her staff also gives her raid-wide cleanse every time she heals, so it should be fun having a few in Bethor or DRag (assuming it won't lag the raid to unplayable, which might happen on taco...)