We've taken both, public from Marigot and GB from the airport.
On the public, if you have any issues with fumes etc, if you have to sit inside, sit on the port side [left facing forward] by a window - the starboard side ports are normally closed due to spray, port side are open
I think if I was staying the Maho area, I might go with a private ferry, overall more $'s, but cheaper cab fare and you get a "free" trip thru the lagoon.
J&B