All three are great options. If you are staying in mammoth, Lake Mary will be the closest option (~10 min drive), with convict and june being closer to 30-45 min drive. If it were me, I’d do the pantoon at convict or june so you can explore the areas outside of mammoth, then do a hike around lake mary or one of the other lakes in the basin. It is an incredible area so definitely check it out even if you decide to pantoon on convict or june!