I have basically been comparing the Pentax 67, Bronica GS-1, and Mamiya Rz67. There's something drawing me to the Mamiya for some reason. I think because its popularity and availability, coupled with the rotating back and hot shoe capability. Prices seem to be fairly close for basic package deals on eBay and keh. I like that I've read more than once the Pentax has great bokeh as I have a serious soft spot for it. I also really like the idea of being able to swap out backs mid roll although not a deal breaker. Man this is a tough one.......
For starters, the size/weight/ergonomics issues with the RB67 as spilled here, and elsewhere, are exaggerated. Your interests--portraits and landscapes--are typically shot on a tripod. The RB67 isn't petite: it weighs in at around 5.5lbs with a 90/3.8+WLF+back. For comparison's sake, a Nikon F3HP+MD-4+85/1.8NAI is only a pound lighter. On a tripod--which BTW doesn't have to be girder-like--the RB is very straightforward:aperture and shutter speed are set on the lens; shutter cocking/film advance are separate but become habit; bellows focusing allows for close-ups without tubes or diopters; the huge focus screen is bright and plasma-like with the WLF and its magnifier; and yes, the rotating back
is the killer feature, since the camera body isn't flipped(a problem with the big Pentax 6x7)for portrait orientation. The RB
doesn't have a hot shoe; instead, flash works via a PC connection on the lens. I shoot mine on the street, at cars shows, and at events on a tripod that I carry. An extra back in a coat pocket and some film and I'm good. It's a superb studio camera. The are several sellers on
eBay offering NOS RB67 ProSD kits now.
Bronica 6x6 cameras have only recently come down in price. I have an SQ-B kit with a few lenses, a 45 degree prism finder+WLF and a speed winder. It's 2lbs lighter than the RB67 Pro S kit I shoot. It's easily shot off a tripod but I often use a monopod on the street. It's probably the newest, most affordable 6x6 SLR around. The GS-1 isn't much bigger than the SQ. It wasn't a huge seller and tends to be pricey
Generally, I'd advise buying the newest gear you can afford. Repair resources aren't as accessible today simply for lack of demand, so the healing powers of the CLA that many of the oldies need(if not extensive repair)just aren't on every corner--or cheap.
Metered prisms for MF aren't that accurate. A handheld meter that can read incident+flash+spot will save $ because it can deliver accurate exposures. The DSLR-as-meter method is awkward and not always consistent.