I owned a GS-1 for years, and tried a RB67 before.
Using an RB67 handheld means in the first line, you have to carry it to the place where you want to use it. If you are always in a studio or if you live in your car and never walk, or if you have an assistant, it's a great camera, especially for macro shots I myself hated it because it is simply too big and too heavy.
Using a GS-1 on a tripod is no problem as long as you use the prism finder. The waist level finder is useless if you want to take shots in portrait mode. It's a great camera, surprisingly small and lightweight, and it's reliable. In winter, take a spare battery with you and get the extra battery compartment. If you are into macro photography get the 150mm macro lens, extension rings are hard to find.