It probably between Williams and Perry.
Perry has experience and crazy arm talent. 13 Passing (14 total) TD to 6 Int as bad as it sounds when you think about how garbage Richt's offense was schematically followed by predictable play calling I'm not sure how much better he could do given his unqualified QB coach while also being taken in and out of the lineup stunning any real chance for growth. Also he doesn't seem like the type of leader a team looking to win 10 games and get back to at least a new year 6 bowl would be off the field.
As for Williams, it just a complete unknown. Instead of thinking about the future and trying to get Jarren some reps in preparation for the 2019 season with the new red-shirt rule Richt continued to play Rosier. I think Williams is talented and it wouldn't shock me if he won the job. I don't think he has the type of arm N'kosi has but I think he could be a more accurate passer.
Weldon might be the fastest of the group but I don't think he has the arm talent either guy has. Also had mediocre stats in HS which isn't a good sign because that might mean his ceiling isn't high, and he is basically here because Richt was doing his dad a favor. Weldon also isn't a good off the field guy.