In the current meta B2 gets a lot of good press but I find that he's a liability. Not long ago I would avoid B2 teams but now I see those teams as an almost guaranteed win because if he's dazed he just kinda stands there .
As a rule, I go by these factors:
-which toon is at the higher gear level
*with the qualifier of which toon is closer to the upgrade (i.e., if Toon A is 2 or more slots away from upgrading to Gear XI and Toon B is one slot from getting to Gear X, I lean towards Toon B.)
Of course this is all contingent upon which toon gets more Arena/Raid mileage.Maybe both have equal value to you,at which point you're back to square one. Hope this helps.