Ally and Neutral Benefit
Ally and Neutral are the most powerful faction in this game.
In Neutral: Abe (pull, cc), Kate (dmg support), Magna (speed), Annie (heal) are a must for builds. R and Sebastian are also good.
In Ally: Andrea (dmg dealer) paired with Sophia can be godly. Put them close. Glenn is also a must as he heals and provides attack boosts. Finally Henry and Shane are very good as well.
So focus on those builds and getting them to mystical and further building along with the benefits.
Don't use all the resources right away, it seems in the beginning we're given a lot but I'm sure it will soon slow down. I typically just pull it daily so to get the daily rewards. Slow and steady is the way to go. I would also recommend supporting the devs as they're great and makes this game very f2p, so occasionally spending $1-$5.