I have a Mamiya Universal system with lenses from 50mm - 150mm. All the lenses that I have are excellent performers, and in terms of sharpness, I can't imagine anything being sharper than the 75mm and 100mm 2.8 (but I don't have a another 6x9 system to compare it with). The 50mm is an excellent and sharp super wide lens. The 65mm is also good, not as sharp as the other lenses, but the images I take with it look good and it's very compact.
The Mamiya Universal is part of a quite large camera system. The backs are very nice, and there is also a Polaroid back available. It is heavy and bulky, and the lack of any interlocks can be frustrating at first (resulting of lots of blank frames, double exposures, etc), but with a little experience it's actually quite nice to use.