Help which characters to focus for multiplayer.

I’ve been playing for like 7-8 years but never took it seriously I’ll usually get on once every 6 months and grind out the challenge and mp season. I know that ares and night wing have the most potential but that’s long term and I’m more of looking for who I can promote and get to level fifty for mp faster. Also is it worth it to get packs until I get the girl green lantern for that team?