I went with Mits over Zim and really I do regret it.
Zims heal link is nice and stacks with other ‘heal over time’ reds you may use such as Red Hood and Ares. People turn their nose up at her weak AoE damage and attack boost being low when compared with other heroes, but Mits is hardly a wrecking ball either in terms of spec damage and a +25% boost is better than no boost. Yes there are other cleansing heroes, but sometimes Rigard isn’t the ideal choice, and a fast charging cleanse is exceptional.
Mits gets some redemption in being the only fire hero with any mana control but it’s not that important, and when her main use is to bait blue enemies into kamikaze dives, you don’t really want to prolong their attack anyway: the reflect is active as soon as she hits, so let them fire at her immediately. In my subjective view, her mana control is the least effective after Chao. In diamond arena, the reflection is fun but heroes like Richard, Thorne, Athena, Isarnia just aren’t enough of a threat to worry about anyway, and Alasie, Magni, Alice have often charged and struck before Mits is ready.
For titan fights, the mana control is OK but the reflect is useless, I would rather have Zims higher attack stat, fast cleanse, attack boost and heal any day.
TLDR; Zim is a boring yet useful multi-tool hero, Mits is niche and unnecessary.