i have kael at 60 so far
If you just have Kael at 60, Deliana is the way to go. Is amazing in early game, and lasts through at least endgame in solid Brutal+ Hydra teams.
After that, we are likely looking at Altan, an amazing defense based damage dealer, with huge upside, and absolute bruiser in Clan Boss, which is your best source of free resources daily as you progress in difficulty.