#1 Samoa Joe

Just when it looked like WWE was finally about to pull the trigger with Samoa Joe, he suffered a minor injury, throwing all of WWE's plans out the window. In January, Joe cut a promo on RAW about dealing with John Cena at the Royal Rumble. Oddly enough, he suffered an injury on the same night.
Joe was also pulled from the Mixed Match Challenge, and while his injury isn't deemed serious, he is expected to be out of action until mid-March. It was originally feared that Joe would miss WrestleMania 34, but the latest word making rounds is that Joe will be back in action a couple of weeks before WrestleMania.
Joe even appeared on Booker T's podcast last month and said that it was a 'week–to–week' thing, which was enough to alleviate the fears of Joe missing WrestleMania 34.
While WWE is reportedly working on a match between The Undertaker and Cena at WrestleMania, a showdown between Cena and Joe could provide a lot of intrigue, and could be a good back–up plan in case the rumoured match between Undertaker and Cena doesn't materialise.
Source: Samoa Joe on Booker T's Heated Conversations Podcast