Unlike the Mamiya RB/RZ, the Bronica GS1 does NOT have a rotating back. This means you have to turn the whole camera 90 degrees to take a vertical format shot (portrait orientation). It's almost impossible to do this with the standard waist level finder. You can use a prism finder to view vertical shots, but it's a heavy camera, and it's not that ergonomically friendly in portrait orientation. Hand held shots in either landscape or portrait mode are much easier on the Fuji rangefinders.
The GS1 needs batteries to power the electronic shutter, while the Fuji doesn't need any batteries since it is completely mechanical, and doesn't even have a light meter. If it's working properly, the electronic shutter in the GS1 should be much more accurate than the mechanical one in the Fuji, however. Due to the electronics, there's a greater risk that a GS1 could turn into a doorstop if it has a critical electrical failure.
Like most rangefinders, the Fuji can't focus closer than about 3 feet, and the newer models don't even have interchangeable lenses, so the GS1 is the clear choice if you need those.