I think either Kiki or Gaston (or Roscoe) would be pretty capable, though I think Kiki would give in to demands a little too easily and/or be intimidated by the pressure and stress involved. Gaston/Roscoe would maybe be too brutally honest with everyone or be too confrontational or standoffish (at first).
Molly. Everyone will be killed with kindness.
Merry. Anyone who puts a toilet right up to their kitchen table would get my vote for mayor.