[user104658]

The WORST endings would be Dany ruling with an iron fist because it effectively makes her a villain and I don't think it should go the "mad queen" route... or Jon ruling because it would be totally out of character as the whole point is that he's a "reluctant leader" and has thus far only accepted ANY leadership role because he needs to, in order to defeat the dead. He doesn't want to be king, that much has been made clear repeatedly, and anything other than him voluntarily abdicating once it's all done just doesn't make sense.

Really anyone actually ruling the 7 kingdoms would be a "bad" ending; most likely I think if both Dany and Jon survive, is Dany taking the "Six Kingdoms" and granting freedom to the North as a separate for Jon - who will then turn down being King and give Winterfell to Sansa as Queen in the North.

If Dany dies before the end then I think Jon may legitimise Gendry as a Baratheon and give the throne to him in a sort of "Bastard Solidarity" move (again, with the condition of the North being free).