Hawthorn if you need a healer or C Hel IMO.
All heroes have different use. You should ascend according to your needs. Nobody can tell you which one is most suitable for you.
C2 Domitia is very good option for titan, C Hel is always welcome, Hawthorne is good healer, Khonshu is good sniper, C2 Obakan can be good tank.
100% what @BirinciKaptan said
A great choice of heroes
Whichever hero you choose good luck
absolutely all of them, you cannot go wrong!
Just work left to right, as mentioned no one can tell you who to work on, however extra healers are a must for the war of 3 kingdoms and that monster island