User blog comment:Monkeyjoe15/Help deciding where to begin with Evolving my units./@comment-24570336-20151208121329

Evolving a 7★ unit as Lead is the best choice because your whole squad benefits from that LS. My recommendation for a leader is:

1. Charla because she offers enormous power with utilities like BB fill rate, status cleanse, spark and crit buffs, heal, etc.

2. Bestie for defensive power through very strong BB fill rate.

Now for 6★ units, you need to decide which unit fills the important roles needed to survive those challenges. Linathan has provided a guideline for players needing help.

User blog:Linathan/Squad Spotlight: Essential Squad Compositions

Hope this helps. Good luck.