#3 Reuniting The Shield
In all fairness, it is impossible to know whether or not reuniting The Shield would have served to get Reigns over in the long run. The reunion was cut short due to Ambrose suffering a triceps injury, putting The Shield reunion on hiatus. The reunion itself was fraught with instability as Kurt Angle and Triple H served as members of the faction while Reigns was out due to an illness.
The Shield was one of the most dominant factions of all time in the WWE. They ran roughshod over the company and the WWE Universe loved to hate them when they were heels and then just loved them when they turned face. Their wars with the Wyatt Family and Evolution cemented their position in history and Reigns was never more over than the time he was with his brothers.
Perhaps there's a possibility of the trio picking up where they left off when Ambrose returns from injury.