So for a while I was playing as "everyone plays a card, then everyone uses a power, then everyone draws a card" which worked out pretty well althought it had it's drawbacks, such as Legacy not boosting damage on one shots.
Now I'm playing in "this character takes a turn, now this character does, etc" but I was wondering... does the turn order need to stay static? In other words can Nightmist who is usually 3rd jump in and say "OMG I have just the thing, let me go first!" or have Unity say "I want to turn your pipe wrench into a robot when you are done attacking with it, so let me go last".
Yeah, especially since it's an official ruling, I think the players need to decide which hero is going in which order at the beginning of the game. It could lead to unfair advantages if you just decide everyone can go whenever they want. Because then you'd just choose the most beneficial turn order every turn cycle. And that's not fair to the villains; their feelings might get hurt.
As I play it, the turn order is rigid. So, Nightmist gets her whole turn, then Mr. Fixer gets his whole turn, then Unity gets her whole turn, and that happens every round, in that order. I put a lot of thought into optimal turn order for my heroes, though. For that group, I would probably be most likely to put them in the order listed above, depending on how many time-sensitive environment or ongoing cards there may be in the game.
Officially, it's each hero takes a full turn, in set order.
Allowing heroes to change their turn order can be very useful to them : having the heroe who can get rid of an ongoing/environment act first, for instance, or having Mr Fixer make all damage to a target irreducible so that the others can destroy it before it can act, and so on. I think it will have a big impact, but do as you wish.
I would not recommand playing "all heroes play cards, then all heroes play power, etc", however, it makes all the "first time in a turn" effects an headache and changes too much the gameplay for me.
I usually put the problem solvers and other support characters early in the turn order, and the more straight up damage dealers more to the end. Works out well most of the time. But I hadn't even considered just being flexible about it. I have a feeling it might be just a little too much power on the end of the heroes, but I'm not actually certain. Fixed turn order does create rather artificial problems at times, so I can definitely see why you'd want to let players choose.
Mr. Fixer benefits from being before Argent Adept in turn order, as it means he can play Grease Gun out of turn and have it actually do something, or Bloody Knuckles/Harmony/a Style/a Tool on his own turn, and Overdrive on AA's turn.
If you allow Heroes to alter turn order then you must allow Vilain to alter turn order... and that would be something really really messy if they start doing that !