#4 Randy Orton
Randy Orton last wrestled for the WWE Championship in July 2017 against Jinder Mahal. Since then he has been in SmackDown Live's mid card and has become one of the top heels on the SmackDown Live roster. He has delivered some of his best work in his career since turning heel last July so he definitely deserves this chance.
He will be great as this match's veteran competitor and it is definitely possible for him to become a 14-time WWE Champion. A rivalry between AJ Styles and Randy Orton that would lead to a match between the two superstars at WrestleMania 35 has been heavily rumored.
It is definitely possible that this match ends up being for the WWE Championship with Randy Orton defending the WWE Championship against AJ Styles. However, it seems much more likely that a match between the two would not be for the WWE Championship, so it is possible but not likely that Randy Orton becomes WWE Champion at Elimination Chamber.