#1 Dean Ambrose
A former WWE Champion, Dean Ambrose has certainly done it all in WWE.
Joining as one of the company's biggest signings from the indies, Ambrose made his main roster debut in November 2012 and has had some of the best matches in the company since then.
Turning heel in 2018 was a great change for Ambrose, whose wacky face run had gotten stale, but this newfound mean-streak hasn't led to the Lunatic getting close to a top spot.
Reportedly unhappy with his position in the company, Ambrose leaving would definitely be a blow to the WWE and his fans, though would be great news for new promotion All Elite Wrestling.
Ambrose entered WWE already a huge star, and if he was to return to the indies, he would definitely be considered one of the biggest draws.