Real Talk: What makes a good batch of Newcomers?

In other words, what makes a selection of newcomers solid as a whole? I ask partially for the sake of my own reworked roster, but also because it's an interesting conversation to have.

Everyone has their own ideas, and I'd love to hear them. I'd love all the details you can give me. How many is a good amount? Are there any philosophies you follow? I seek answers, gamers. As always, thank you in advance for your answers!