I suppose it depends on the direction that WWE still wants to go in. If Brock Lesnar vs. Roman Reigns has to happen again, I'd much prefer a SmackDown guy to win the Rumble. Say, Shinsuke Nakamura. Then he challenges AJ Styles. That would be fun. Can you imagine if Jinder Mahal wins the Royal Rumble? The crowd would go insane.
Generally though, I really can't put my finger on one guy this year. Nobody but Reigns stands out, but surely they cannot do a repeat again. The same building, the same event, the same match. They've already made that mistake once. A guy like Seth Rollins or Kevin Owens could really benefit from a Rumble win too, to propel them back to former heights.