AJ Styles (140 Days)
Styles was red-hot when he won the WWE Championship from Dean Ambrose at Backlash. Previous attempts to win the title from Roman Reigns were less successful, but Styles was riding a lot of momentum. He had just come off a victory over John Cena, so the time was right for him to win the title.
Styles feuded with Ambrose for pretty much the rest of the year. He also defended it against top superstars such as Dolph Ziggler, Baron Corbin, and James Ellsworth. Together, he and Ambrose carried the main-event scene of Smackdown, and they don’t get enough love for it.
At the Royal Rumble, Cena got his win back over Styles and became WWE Champion, ending Styles’ run at 140 days. Meanwhile, Jinder will now hold the title for at least 182 days, so he’s left Styles behind in the dust.
Such is life.