Hm. That’s tricky. For PvP, mixing things up will always serve you well. Defense teams are typically composed of heroes that work well with each other. Just think of teams made of pairs that go really well together then you add “filler” characters that work well with everyone.
Main pair: Elsa+Olaf
+Filler heroes: Mickey, Moana, Maleficent
= Full Team
For Coliseum, you have to make this stuff 3 times. Then for offense, you then consider how to counter the opposing defense.
With the above team in mind, you might want to do:
Main pair: Hercules+Megara
+Defense counter: The Mad Hatter, Darkwing, Kevin Flynn
As for PvE, like in City Watch, Invasion, etc, healing is a huge boon to your chances of success. As far as offense goes, heroes who have “build up” are the absolute best characters to invest in.
So that said, take into consideration:
- Nick: Essentially unstoppable when he gets 5 lemmings.
- Zurg: Once his energy is full, he can sweep wave after wave almost tirelessly.
- Hercules: His HP will continue to rise and can even become invincible.
- Alice: For the same reasons as Zurg and Herc, albeit to a slightly lesser extent. Still terrifying though.
And then you have your healers, who are absolutely necessary for keeping the whole team topped up.
- Sulley: With Woody’s disk, he heals the whole team at least once in the middle of battle and again at the end of each wave. Works so beautifully with Nick and Zurg, but struggles greatly the farther you go during Invasion.
- Mickey: Wonderful healer overall and his damage boost benefits everyone. May struggle to heal by himself sometimes. You also have to be sure that he is at least the same level as everybody else or he’s dead weight.
- Miguel: By fat the most potent and most reliable healing, especially with Jessie’s disk and while playing in manual. You may find your team dealing far less damage though. Very noticeable against later bosses in Invasion. Be sure to use any available debuffs at your disposal.
- Genie: Marvellous healer whose healing is instantaneous. The invincibility and extra energy he provides is just fantastic and he even contributes a decent amount of damage too. However, he can’t heal himself and may need another healer’s help.
EDIT: In the end of the day, you play your favourite heroes as often as you can allow. Pair them up with heroes that cover up their weaknesses then go from there.