I would recommend sitting on those Tabards if you think there is any chance you pull either Jabberwock or Clarissa, who are both going to be clearly better options for you.
If you feel you must spend the mats ASAP, I’d personally rather ascend Victor or Grimble, as I find Kunchen by far the easiest high level tank to deal with with his slow mana and generally passive special. If your alliance runs dark tanks he is still the best option you have, but short of that I’d rather have another very fast hero on offense or a tool to deal with the increasingly minion heavy meta.
Kunchen is among top heroes in the game, not only for his tanking ability (looks that your purple in def is crowded already) but offensively as off color healer he is amazing. Major difference from Rigard.
If you are stubborn to not want him, that’s fine. Then go with Victor. Defense buff at very fast speed, together with your other very fast Kage for stacks, is going to be great.
Grimble and Domitia are not recommended. People say Grimble works now well against Telluria tanks - well probably these people never tried it, I tried and he still sucks. Domitia is pretty outdated, and you already have Seshat who much better fills that role better.
Kunchen then Victor. But since you have Seshat and Kage, you can also wait for Killhare (Springvale), Alfrike (possibly next Valhalla) or Clarissa (May HoTM).
As you are currently quite okay with purple, you could probably hold the tabbards for a couple of months as there are a few viable heroes coming.
If you’re in hurry, Kunchen or a 2nd Kage will be just fine. Grimble is meh. I’ve known few who keep grumbling over maxing Grimble.
Sound advice from people above. But, I’ll ask what’s your focus? If you like titans -kunch is your wisest. The only other hero if you don’t want a five star dark healer is Victor- very fast and good on offence for wars. Don’t max a second cage- emblem up your first one. And yes, possibly wait for Clarissa who’s going to be the dark GM and probably good everywhere. In all of this consider the classes for emblem allocation ( emblems are my final decision to go on good heroes so- victo, kunch or Clarissa depending who would get emblemed up the fastest)
Once you get rigard’s costume, kunchen will take a backseat… but if you run purple tanks, he does have value. I’d def wait a bit before deciding. Clarissa looks like a favorable choice.