Defensive arena team

Obviously it depends a lot on whether you are putting money into the game. I have found that early in the game, there are very few good attackers so healers/tanks play a bigger role. Also most people who start playing the game (like me) had no idea how complicated everything is and just start collecting characters they like or they get a lot of shards for.

The advance groups seem to be focused heavily on speed and offense. Arena battles are over in a few rounds as the early arena battles can be pretty long.