It depends! You’ll almost always fire Boldtusk first (there are exceptions where you might not - Wonderland hero debuffs that refresh with healing and Morlovia heroes that steal healing).
The rest depends on the health of your targets. If you want to distribute damage evenly, then you go Wilbur, Falcon, and either Mitsuko or QoH fourth and fifth. It’s important to hit the same three targets with all of your hit three attacks to maximize damage.
There are certain situations where you may want to take out particular heroes who might survive if damage were shared but would be knocked out if targeted directly. It’s a smaller chance, but it’s possible since you don’t have any burn damage to finish off stragglers. In that case, you may want to leave Wilbur for last. And focus on the three you want to take out as highest priorities, firing Falcon and then the two ladies.
Also, you may want to fire Mitsuko after QoH as a general rule so that you can target her mana cut where it’s most needed in case you can’t finish off a hero with the damage.
P.S. I apologize in advance to @Boolz_San_CK if you’re not looking for anyone else to answer questions in this thread. It is your thread after all.