Optimal, based on this chart:
||Rest Strong color
- Kiril or bear banner for +att boost.
- Grimm is avarage and Isarnia is slow, but Isarnia att stat 797 (no.1) and Grimm is 716, so if you have good mana troop and or use mana pots or Tornado, best use Isarnia.
- You have Arthur must have slot.
- Miki best stack for blue of course
The rest priority is best tile damage and some survive support for Titan *11 and up.
Kiril - Isarnia - Arthur - Miki - … (last only one slot: Ariel/Aegir/Magni/Alasie)
Aegir attack stat only 615, and Kiril is 656, and has bonus att buff (this is important slot).
Ariel attack stat 731 and Magni is 793 (but magni only +def nearbly and already used the better slot one Kiril).
Ariel mana generation has more usefull here.
So, based on theory, the 5th slot should be Ariel, I will place like this from left to right:
Kiril - Isarnia - Arthur - Ariel - Miki
But you can also try which is more has advantage and survive with this:
Kiril - Isarnia - Arthur - Magni/Alasie - Miki
here, Magni/Alasie skill should hit very hard, well but the most value is from tile damage though.