Probably Ariel for the mana regen
Kashrek. Period. 45% heal with high health and easily obtainable. 
As coming back to your current 3. It depends on what are your other heroes to go along with the healers you listed. All 3 are great and able to flip the raid around when they launch.
Ariel has average mana. 'Nuff said
My vote goes to Ariel 
I guess it would depend on the rest of your team. I often run attacks with Isarnia, her defense down doesnt match with Kunchen so Vivica is the more obvious choice.
If Id use Magni, Kunchen would be a better fit than Vivica.
I don’t have Ariel, but I can see she is useful. She fires quicker. But for me personally, Kunchen and Vivica are bigger game changers when/if they actually get to fire.
one thing to consider is if a high level mana troop is available, average get charged from 10 to 9 tiles which is massive change, which is very close to fast. This is much more significant than going from 12 to 11 for slow heroes.
1 Ariel
2 / 3 Kunchen Vivica .
You are super lucky . I only have Kunchen and spend 18 000 diamonds to get Ariel , no luck , no Vivica either…
Ariel. I can’t bring myself to use slow healers
Ariel is the best healer
Ariel gets my vote. She’s a game-changer with all fast/very fast heroes on the team
Ariel - she’s average mana user and not forgetting she boost other heroes mana fast which is important. Great luck to have all 3 healers to be honest. Congrats! 
No healer does as Kunchen do, eaven if is slow mana he can live alot to fire 3 or 4 times before he dies and if you have the proper troops you can increase the mana to avarage so in my opinion his the most useful here
Ariel is better than Kunchen, considering the hero and only the hero (and I have both). Average mana trumps slow mana, and the mana generation is absolutely fantastic, Ariel has great synergy with any hero formation. But Kunchen is good too - it’ll depend of your roster, on who else you have.
If you have another defense debuffer (Isarnia, for example), Kunchen becomes somewhat redundant (even though he also cleanses).
Kunchen 1st if you talent grid and get him up his defense and health takes to long to kill him by that time he used his special atleast twice which minuses defense front the enemy but not to say Ariel’s isnt good I have her close 2nd because of mana speed and mana boost
But costume vivica is a beast which if you have her she jumps to maybe the top spot
So I thought I would drag this up from the dark. With Soul exchange out now, I’m looking to try and update my healers. First question 1: Who is the best healer in each colour 2022? and 2: what healers do you think would realistically be in soul exchange?
My healers are Boldtusk, Kiril, Melendor, Vivica and Sabina (I can’t seem to get Rigard C). I can’t imagine any healer being released in SE that would be better than these guys. Thoughts?
Ariel, no doubt about it by far. Even cRigard is better then Kunch.
Ariel for her mana speed and you could set yourself up for the costume if you ever pull for it.
I think there are several very strong contenders for this title:
Ice: C Ariel, Milena, Passepartout
Fire: Garnet,
Nature: Toxicandra
Dark: Xnolphod, Hulda, Diaochan
Holy: Director Zuri, Prof. Lidenbrock
And probably there are a couple more that slipped my mind this time…