Here's mine:
My thought is way too often team books, don't leave much room to tell character driven stories that has time to focus on their histories, powers, character, or giving them a narrative a place to start or end. I think the above team has the profile, interactions, and familiarity to combat most threats, is classic X-men, while making a complete team.
You can also choose a supporting cast if you like but your five character will make up the team and will be the focus of your hypothetical book. Think in terms of NXM: