Hi Rob,
In the 1970s, before the GS-1 came to market, I was a tech rep for Bronica (and Mamiya). I currently own and have used the GS-1.
Later, again, in the 70s, I served as a sales rep for Honeywell-Pentax for the Northern California territory ... so I know the Pentax 6x7 as well.
They are both superb cameras and I want to to agree with several points already made by some of our colleagues, above, and add a couple of reminders that have been overlooked:
,
• As always, when buying second hand equipment, I agree that availability of parts and service should be a primary consideration. The Pentax has a certain advantage —compared to the Bronica GS-1— that there were so many more units sold (and so more "spare parts" available in the field from old bodies, etc.).
• The Pentax might be a better "around the neck" camera, as a hiker .. I dunno. (I carried my Bronica EC-TL —another brick of a camera!— around my neck for street photography for many months, and it didn't really bother me much). However, a zillion fashion photographers can attest to the easy handling of the Pentax, especially with its add-on (and cool-looking) wooden handle.
• While Bronica has about 9 lenses for their GS system, Pentax has a much more extensive system, with something like 17 lenses (if memory serves), including a fish-eye, a shift-lens and a 1000mm telephoto a copy stand; a slide copier; a lens adapter (to permit mounting 6x7 lenses onto Pentax 35mm models), etc, etc, etc .. (if you need all that stuff!)
In the face of all that, I believe that the Bronica GS-1 deserves a little 'sales pitch', as I really agree that it's an under-rated camera (and I absolutely pray that my remarks here won't contribute to driving up its price!)
Bronica GS-1 advantages vs Pentax 6x7:
• There's a "camera rotating device" available for revolving the camera while its mounted on a tripod without changing the lens axis position relative to the subject being photographed
• The GS-1, is not just a "6x7" camera; it is truly a multi-format camera thanks to its a system of interchangeable film backs in 24x36mm (35mm); 24x69mm (35mm panorama); 6x4.5cm; 6x6cm; and 6x7cm. (I'm not including 220 and Polaroid backs, for obvious reasons) Beyond the advantage of allowing different formats from one camera, this option also gives you the possibility of using two different types of film, for the same shot, and to photograph the two shots in tight sequence -one right after the other- without the delay of changing film.
Especially because of this last point (multi-format) that the Pentax 6x7 —as good as it is— essentially isn't really directly comparable to the Bronica GS-1. Please don't misunderstand this to mean "the Bronica is better". I simply mean, it's different. It corresponds more closely to the Mamiya RZ. Therefore, I believe that you should closely mull over your needs before deciding. As Ansel might've put it: Visualize your use!
I really hope this helps you decide.
Best,
Christopher Nisperos