If Lesnar vs. Reigns is still the ultimate plan for the Universal Championship, then it'd be a massive waste of time for Reigns to win the Rumble because everyone has known that this match has been coming for months, a lot of months, so I'd rather see someone from SmackDown get the win.
As to who it should be, I wouldn't mind seeing Nakamura get the win and face off against AJ Styles for the title at WrestleMania. As for someone other than Nakamura, I think it'd be fun to have either Owens or Sayn win the Rumble, though there's no telling how long they'll be in the doghouse after being sent home from the European tour. As of a few weeks ago, the plan was for Cena to referee Jinder's match against Lesnar next Sunday with Cena accidentally costing Jinder the match, thereby leading up to a match between them for WrestleMania eventually. However, that's all up in the air given that Cena is now part of Team SmackDown due to Styles winning the title from Jinder. There's a strong possibility that Jinder regains the title next month during the India tour, which means Styles will get his rematch at the Clash of Champions ppv; if Jinder regains in India and retains in the Styles rematch at COC, then I think there's a strong chance, unfortunately, for Cena to win the Rumble so he can beat Jinder at WrestleMania and get his 17th World Championship win. IF that ultimately turns out to be the plan then, in my opinion, it's just an uninteresting main event scene all around for WrestleMania next year due in no small part to the outcome of both matches being all but guaranteed already.
"What Do I Know Of Cultured Ways, The Gilt, The Craft And The Lie?
I, Who Was Born In A Naked Land And Bred In The Open Sky.
The Subtle Tongue, The Sophist Guile, They Fail When The Broadswords Sing.
Rush In And Die Dogs - I Was A Man Before I Was King."
Conan Of Cimmeria