Double ply Swampthings at low pressures are ace when it's truly awful out; one on the back digs like crazy - but is slow, squirmy and rough on hard surfaces.
IME Barons are at least as grippy as Swampthings in mud, better everywhere else. don't squirm, roll way better and last really well.
I am going try a Barron on the rear of my FS see how that compares
Watch yourself on muddy corners with them that way round. I'd tend to suggest Baron on the front if you are only ruunning one but it depends whether you are having problems with cornering or propulsion.