#3 Worst Option: King Corbin
I do think King Corbin is a future Universal and/or WWE Champion. I just don't think him taking the title from The Fiend would work within the canon of the WWE storytelling universe. When he does win the title, it will have to be against an unquestionable babyface, someone similar to when Kofi Kingston held the title. It would garner Corbin nuclear heat and that is something that he has proven to be great at handling.
Corbin is one of the few true heels in WWE whereas The Fiend is supposed to be a heel. He's so good at his job, however, that a good portion of fans love him. Having a hated heel take the title from Wyatt, regardless of how good he or she is at their job, would probably backfire on someone like Corbin.
He's had a good run as one of the major heels on SmackDown and the King topped the Big Dog at TLC with loads of help. I don't think, however, that he's likely to come out on top of Reigns once all is said and done. They've given Corbin some pushes in the past, like winning Money in the Bank and winning the United States Championship. His time will come in the future, but it shouldn't be at the expense of The Fiend.