#1 Roman Reigns

To the surprise of almost no one, Roman Reigns is the favorite to win the 2020 Royal Rumble. He's been kept in the mid-card so as not to get the fans to turn against him with his constant pushes and title shots. It has worked to a degree as the crowd has cheered for him more since his return from illness than they did prior to his journeys to the WWE and Universal Championships.
It's helped that he's feuded with one of the most despised people in the whole company in King Corbin over the last four months. It's easy to cheer anyone who opposes the King and it's helped Reigns regain some momentum with portions of the WWE Universe.
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The Big Dog has been in the final four in 2016, 2017 and 2018, so there's no reason for him not to be in it this year. WWE might think that the entire crowd will accept him if he wins, but if he eliminates someone like Kingston or another fan favorite, it might backfire for them. That's a big reason why he'll likely be joined by King Corbin at the end of the match. When Randy Orton won in 2017, his win was met more favorably because he eliminated the golden boy in Reigns. For the same thing to happen, someone the crowd doesn't like needs to be a part of the final four if the Big Dog is going to win again.
Conclusion
There are several other Superstars that could feasibly be a part of the final four. Lesnar could last until the end but it would be better for him to get eliminated at least half-way through so that other stars can get focus throughout the match.
Rollins could make it to the final four again because he's one of the biggest Superstars in the company and now one of its top heels. He's quickly getting the crowd to hate him even more and more each week. It's amazing to think that he's the guy who many wanted to win the whole thing last year.
Others like Orton, Styles, Braun Strowman and Kevin Owens would also make sense as men who could come close due to their places on the roster of either RAW or SmackDown. One other thing to consider is that we don't completely know the entire field of the match until it actually happens. While I personally don't believe that CM Punk will be a part of the match, it would be a pleasant surprise if he was. We can't know the entire game because if we did, it would be boring and predictable.
Several Superstars from NXT could also be a part of the match even if each brand isn't getting 10 spots each as previously rumored. A lot can still happen in the time between now and next weekend. There are some bread crumbs to follow as things aren't as secret today as they have been in the past.
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