I had the same dilemma for Ares and Zim. Went Zim and then eventually Ares. Wish I hadn’t dropped the rings on him. He’s not a defensive tank anymore, he’s an offensive enabler but is not really anymore effective at 4.80 then he was at 3.70. Paladin talent is a gimmick beyond the stat increases. Zim at talent level 2 holds cups way better than Ares at the same.
For the Greens I’d hold off as there is a HotM in May or June that you might really like. Very fast mana currently and a unique special.
Blues - well I’ll always recommend maxing elemental defense downs as a priority due to the longevity they will have in your rosters (foreseeably forever).
Correct me if I’m wrong but you generally see the HotM follow a set colour chart i.e. Khiona, Aegir, Zim, Evelyn, Onatel, Kunchen, Frida, Red, Green, Yellow…