#1 Batista

When Batista returned in 2014, it wasn't a good run. WWE made it very obvious that he was going to win the Royal Rumble. After fans were demanding Daniel Bryan to be in the main event spot, plans changed for Batista. He would lose three PPV's in a row and then leave.
He left to have a pretty good movie career, but the itch to come back has gotten to Batista. It's not a secret that he had an interest in returning, so let him. But the only request is that he shouldn't be shoved into the main event scene right away.
Did you know a top WWE Superstar just wrestled outside the company? More details HERE
If he were to go to RAW, let him feud with the likes of the Miz or even Braun Strowman. On SmackDown Live, he could feud for the United States Championship, whoever that may be if and when he comes back!