I've used in various capacities the Makina W67, Makina 670, both Fuji GF670 and GF670w, Fuji G690BL and GW670iii, and a full Mamiya 7ii kit.
Hands down the most used one was the GF670 because AE exposure and compactness means it gets carried to trips almost as an after-thought. The 690s are so huge they force me to sacrifice room in the bag that would otherwise have carried a second camera. The Makinas are great as they fold down more compactly than the Fuji's but are slow to use and focus - benefit is in being able to put filters on them easier compared to the GF670s. The Mamiya is the ultimate kit, probably the most clinical sharpness of all, but not exactly compact either.
It's a good compromise for system flexibility, weight, and quality if you could deal with the slow-ish normal lens (F4) and non-folding. The Mamiya 7ii I had though, required calibration / collimation for the lenses I had as the rangefinder could go out of alignment easily and the 150/4 especially needed to be precisely aligned.
Usually I opt for 6x7 as the format is pleasant (about 5:4 aspect ratio) for portraits or landscapes and crops down nice to 3:2.