Based on POLL: Who is Better - Maxed Hero with MCB or Maxed Costumed Hero, this resulted to:
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It appears that the maxed costumed Kiril is preferred by most of those who participated in the polls since you have the ability to debuff attack and defense of all enemy heroes, making them a bit squishy and attack a bit softly, allowing you to kill them a bit easier and better survive their attacks. Personally though, I would max both and emblem one based on the original version opting def>health>att nodes while the other emblemed based on the costume version opting def>health>att nodes. But I would emblem first the original version since I have Athena handling the enemy defense down. Problem is, the costume is evading me for several months now and getting it gets murkier soon with the introduction of new costumes of other S1 heroes.