I have both a Rollei 3.5F 12/24 Planar and a Mamiya 7II. Both are extremely sharp. I use the Mamiya 7II much more frequently and particularly on a tripod with the Kirk L bracket which allows for switching from horizontal to vertical without incident. The Mamiya 7 lenses are some of the sharpest ever designed for medium format; I have the 43mm, 50mm, 65mm, and the 150mm lenses. Very small, light, compact, and quite system. But it does have some limitations for close focusing, usage with the supplementary finders for the 43mm and 50mm lenses, smaller finder for 150mm (without the 150mm supplementary finder), lack of DOF preview, inaccurate markings on the lens barrels for hyperfocal (off by about 2 stops), difficulty in using grad filters, but doable, etc.
Rich