#1 Randy Orton

This potential induction is more of an indication of when and not if. Orton, like Cena and Batista, was a hugely dominant and successful part of the WWE from 2002 until 2015.
Batista and Cena have come and gone a few times in that time period but the Viper has remained loyal to the WWE since he debuted in 2002.
Over that illustrious career, he's captured 13 World titles, a MITB win, two Royal Rumble victories and numerous other accolades. He's a consistent main-event presence on whatever brand he's a part of. The funny thing is he's perhaps doing his best work currently in his ongoing feud with the returning Edge.
Whenever Orton has switched from heel to face and vice versa, it's been hard to see much difference in his character.
All he usually does is target faces when he's a heel and heels when he's a good guy. But in this feud with Edge, he's clearly a reviled villain and it's easy to see that Orton is enjoying this run.
The Viper has also battled everyone from Triple H to Cena to Batista to Bryan to Styles and the Undertaker. He's also had memorable feuds with Chris Jericho, Shawn Michaels and practically everyone who has come and gone in WWE. There might even already be a spot reserved for Orton, he just needs to retire first for an induction to become official.