#1 Rey Mysterio

Rey Mysterio returned to WWE at The Royal Rumble last year in one of the biggest shocks of the show, before he later signed on to make a full return to the company. The current United States Champion has had a number of issues with injury since his return, but it has allowed him to bring his son Dominic into storylines with the biggest company in the world.
Mysterio has noted a number of times that his dream match would be against his son so that he can hand over his mask and retire a happy man. If WWE is able to wrap up Mysterio's current storyline with Brock Lesnar at The Royal Rumble, then there is nothing stopping Mysterio and his son from going one-on-one at WrestleMania.
If Dominic betrays his father in his feud with Lesnar then this feud could come to a head at WrestleMania and Mysterio would then be able to support his son throughout his career with the biggest company in the world.
Mysterio looked as though he was going to retire on an episode of RAW earlier this year, but his son convinced him to stay so that he could one day wrestle him, which makes this the perfect farewell match for Mysterio.