#1 Cedric Alexander
Of all of the stars on WWE RAW, Alexander makes the most sense to me as someone to add/join the Monday Night Messiah. He's proven to be a great ring worker and popular when given the chance. His feuds with AJ Styles and Drew McIntyre showcased him going up against larger stars and more dangerous groups like the OC.
Alexander has been used primarily as enhancement talent lately. Reports emerged lasy year that said some backstage don't see him as a big star. But whenever he's been given time to shine in a competitive match, he delivers. He's quick, agile, strong and sudden. That doesn't always lead to success in wrestling, but Alexander did have some backing from Paul Heyman before things changed.
If WWE decides to use him in a different manner, they could easily pair him with Rollins. He's probably looking to move up the card and joining the Monday Night Messiah could provide him the opportunity to do so. They could even play on the history he has with Murphy as both were stalwarts of 205 Live and are former Cruiserweight Champs. Heck, Murphy could even be the one to "recruit" him. Rollins is going to need reinforcements and Alexander is too talented to sit on the bench. It would also allow him to act as a heel in WWE for the first time.