#1 Braun Strowman

Braun Strowman has had a very weird year. He started off in contention for the Universal Championship, wrecking carnage on a regular basis. He then dominated the Elimination Chamber match before losing to Roman Reigns in the end.
After that, the Monster turned into one of those fun-loving babyfaces, basically the John Cena type. He won the Raw Tag Team Championship at WrestleMania, alongside a child. While Nicholas also technically won his first championship, Strowman's first taste of gold, or silver, came at that time.
After vacating the titles on the Raw after WrestleMania, Strowman would win the Money in the Bank ladder match. He was guaranteed to become Universal Champion either way, but somehow he did not. He even turned heel to be a foil for The Shield, despite remaining ridiculously over.
The Monster Among Men failed his cash-in when Brock Lesnar invaded his Hell in a Cell match against Reigns and failed to win the title at Crown Jewel as well, losing to the Beast again. It is baffling that the only championship that Braun Strowman won in 2018 was the Raw tag belt. And that too with a 10-year-old kid.