The word "should" is very subjective. We've heard dirt sheet rumours for a while now that the plans are for Reigns to challenge Lesnar and Cena to challenge Mahal. This would dictate that either Roman or John are winning the Rumble.
The Royal Rumble is returning to Philadelphia, the same arena and crowd that boo'd Dwayne Johnson and Roman Reigns out of the building three years ago. The Shield reunion is in its infancy, and they're finally doing the right things with Reigns.
He's been short spoken, he hasn't been the centre of attention, and he's dropped those awful brightly coloured vests. Will that be enough to have him cheered two months from now when he's been absent for a month?
Cena has been largely out of the title scene. He just put Roman over and perception of him has altered changed. Is that enough to keep his win exciting? Cena winning would put him alongside Austin as the only triple winners in Rumble history. The triple win could go along nicely with the road to his 17th world title.
Obviously it seems some plans may have changed. AJ is now the WWE champion, and Cena vs Styles in an absolute barn burner screams WrestleMania more than Cena vs Jinder Mahal.
Cena is a five star match guy with the right opponent. AJ Styles is the right opponent. Wouldn't it be better to have a memorable match coincide with the record breaking win than a forgettable average match with an average worker like Jinder?
Mahal as a character is far more interesting than the man playing him is skilled as a wrestler. WWE will have difficulty resisting the temptation of having a good old American boy challenge an evil foreigner at WrestleMania.
If Cena wins, they have to make it hard for him. Maybe he enters at 1 or 2, maybe he's got to earn his way into the match. The only challenge is there isn't anyone around to play a thorn in Cena's side. Bryan and Shane are babyfaces. The heel authority figure is played out. For Cena to win and not be met with indifference, there have to be stakes greater than the match itself.
Who should win the match? Styles vs Nakamura would be a dream match. Braun Strowman is very over. What if all three Shield guys tie ala Lex and Bret?
What about Nakamura jumping brands like Benoit to set up Brock vs Shinsuke?
I'm a huge Nakamura mark, but I don't see him working into a world title scene until late 2018 at the earliest. He's just been used to put over Mahal, he's in a multi-man match at Survivor Series, which is now basically bragging rights. He has one event to pick up a major win before winning the Rumble? I'd love to see it, but his main roster push hasn't compared to his NXT run.
Nakamura should win, it would be nothing if not fresh and the match with Styles would be a MOTY candidate. Cena most likely is scheduled to win and secure that 17th world title. Hopefully they find a way to make it feel like they're not going through the motions. Cena vs Styles would be an emphatically better consolation prize over the blandfest that Cena vs Mahal would be.
Roman can be ready come WrestleMania to at least get a Cena level mixed reaction. He won't earn the mixed reaction if he goes over in the Rumble, he'll still be booed.