Fultz and Griffin.
Though I'd sign Hayward if we have the chance and Griffin is a no-go, we'll still have to find a starting frontcourt piece if we sign Hayward, which isn't the same story as signing Griffin, who plugs in perfectly to our needs.
I don't think we can permanently play small with IT, AB/Brown, Crowder, Hayward, and Horford in the starting lineup.