Currently my favourite characters are:
Bucky (Winter Soldier) - useful for dealing damage to tanks as they move towards the objective/rest of the team and good combos against DPS/healers.
Invisible Woman - has taken over from Mantis for me as can solo heal a team with her and also contributes a lot to DPS.
Scarlett Witch - the easiest character to use on the game imo but also quite cheesy. Have to be more strategic with ultimate ability as easy to get shot doing it.
Also like Moon Knight, Iron Fist, Squirrel Girl 🙂
I usually avoid tanks as not my strongest point but I’ve also not really used any yet.