#1 Isaiah "Swerve" Scott
Every group needs a high-flyer that can pull off some jaw-dropping moves. Like Thorne, Scott is a daredevil and isn't afraid to throw his body all over the place. If you saw his work in Major League Wrestling, Evolve or Lucha Underground, then you saw what he's willing to do in order to put on a great match for the audience.
While he didn't get to showcase a ton in the Breakout Tournament, he is a versatile Superstar like Seth Rollins. He's fast, quick, tough and can speak. He's not Kevin Owens or Paul Heyman on the mic, but he's good enough that he could be the voice of a new incarnation of the Shield.
The dynamic that made the first group work was that Ambrose was the unhinged wildcard, Reigns was the silent assassin and Rollins was the work-rate dynamo and "Architect". Swerve would be perfect for the Rollins role as he is also someone who has a lot of street credibility from his time on the independent scene.
If I was in charge of picking stars to reform the group, I'd start with Swerve. The only thing working against him is that he's already appeared on 205 Live. While the majority of the WWE Universe might not follow that show, a good portion of it does. It would be best to use stars who've had very little exposure to the main roster.