He's not Daryl because she's dead and he's a guy (Confirmed)
You don't know that Daryl is dead, only the wreckage of the Falcon was found(no body), and where is it confirmed that Gogo is a guy?
He's not Banon because Banons weak
Banon's not weak, he's a great healer, and there's no reason to not believe that he can be Gogo.
He's not Gestal because Gestals evil!
Still, Geshtal might want revenge on Gogo, hence his watching the affairs of the world, and now he's ready to exact that revenge.
(Or maybe That presedent ^_^)
But of course he's Adlai Stevenson.