Hi Clint-- I have both the Bronica RF and the Fuji GS645S. You might scan over some past discussions here for previously posted views on this subject.
I can say the Fuji is smaller and lighter and more delicate. Unseen and unknown to me at the time, when I got my Fuji used it had broken plastic parts in the lens mount. I guess that's why there's that "bumper" there, but it got broken anyway. :-(
Other than that, the Fuji is a great little camera. It has one advantage over the Bronica in that the viewfinder framelines shrink as you focus closer to match what the film will see. Both cameras have continuous automatic parallax correction, but I don't know of any interchangeable-lens RF cameras with frame-size correction too. The fixed-lens Fuji has it, the Bronica doesn't.
Both have good viewfinders, but the Bronica has a better RF spot that is crisp-edged and contrasty. The Fuji's RF spot is fuzzy around the outside and has less contrast.
Of course the Bronica has your choice of manual exposure, aperture-priority AE, and Program AE. Fuji is manual exposure, and the light meters for both are in the viewfinder window area.
Both cameras are easy to load, and will take 220 film too. The Fuji gets 15 shots on a 120 roll, while the Bronica manages 16. The Fuji crowds a lot of controls on the lens barrel, so you have to learn their positions and feel in order to work quickly and surely.
The Fuji's shutter is louder due to what I think is an artificial noisemaker built in. Makes a "CLACK" noise as you trip the shutter. The Bronica has an odd buzz-wheeze that occurs right after the exposure; this is the electronic shutter recocking itself.
All the lenses are great. But the Bronica's viewfinder doesn't display framelines for the 45mm lens; for that there's an external accessory viewfinder. I've just been using the whole VF window as approximate 45mm framing, but without parallax correction I do lop things off. Using the 65 or 100mm lens is handier than the 45.
They each have their advantages!
