In my mind, a balanced character is a character that has obvious and defined positives about his kit, but significant cons to counteract those pros to a certain degree.
Acceptably balanced characters:
4 star:
Nick Fury
He has high damage, high utility and can do a lot of things. But he has high AP costs, relatively low health and his highest damage ability is unreliable. That’s what we in the business call having pros that are balanced with cons. Unlike a few other 4 stars who had high damage, high utility, high health and ability predictability paired with relatively low AP costs. Or, on the flip side, characters that have so many cons, their one or two pros don’t mean anything.
3 star:
Deadpool
High damage on Red but can’t be a finishing move. High damage on purple, but it is high cost. Low health and limited sustain. He is also a model of pros balanced with cons.
Daken
Great regen. Great strike tiles for whittling away at your opponent. Low health and no truly impact ability. Plus he has the capability of slowly killing himself with a bad board.
Patch
Great regen. High damage on red, but high AP cost as well as requiring him to tank colors. His green is the perfect example of a high risk high reward ability. Perfectly balanced.
Loki
He has clearly defined pros. His ability to steal AP when you play hastily against him is incredible. His purple being able to reset a bad board is also clutch. His black has a great niche purpose that could come in incredibly handy in certain situations where most characters would be rendered helpless. Cons include low health, no actual damage and reliance on the opponent to use his best ability.
Luke Cage
He has a clear niche as a high health defender who can be used to reduce match damage for longer climbs. He has 2 high impact damaging abilities, but they are off set by the high AP costs and (1) the reliance of having a special tile on the board in order to deal any heavy damage with black and (2) the requirement of having your team alive when using his yellow. He does drag out defensive fights a little too long, but overall he isn’t oppressive nor is he useless. Very well balanced.
Classic Magneto
Another very well balanced remake. He has high damage, high board shake and some good protect tiles but he has low health and a majority of his damage is reliant on the state of the board (need enough red and blue to swap for blue and need enough TU tiles for red to be worth it). He may be slightly on the overpowered side, due to his destructive nature, but he is very beatable with 1 or 2 abilities.
Captain America
High AP costs and useless yellow are his weaknesses. High damage and stun with relatively reliable AP return are his strengths. He is, in my opinion, the perfect example of balance in this game.
2 star:
Thor
High damage abilities off set by high AP costs. He was designed as a 2 star character. Buffing him up to 3 star made him a little overpowered, but this incarnation of Thor is very well balanced.
MN Magneto
High utility offset by a relatively worthless blue and red ability. But his purple is enough to make up for both of those abilities. Strong, with good partners in both 2 and 3 star land, while simultaneously not overwhelming any scene.
Storm
Another character with clear strengths and weaknesses.
Other than these characters, I believe each character is either too far on the strong or weak side of the spectrum.
There are a few other characters that have special niches: Dr Doom and Daredevil are fairly good with Patch. Hulk is great for hulk bombing with Patch as well. Mystique is a great PVE character with winfinite and Blade is also good for taking out PVE nodes.
Cyclops is one character that may be balanced. I don’t know because I don’t have him leveled and I’ve never seen him in PVP. We’ll but a TBD on him.