Ares is a better standalone hero, Zimkitha can’t sustain herself but help with a full status aliment removal and empower the attack on top of that.
If you have troubles against Zeline & CO. then Zimkitha, if you need a red tank for alliance war or you lack red heroes for titans (Zim is worse than Boldtusk here) then Ares.
Id say that Ares sure is nice to have but a fast cleanse is gold.