They are so far apart that is hard not to laugh, but, in the spirit of cooperation I'll say they are both excellent cameras. Rollei: German,6X6, light,fixed lens, easy to take on a trip. Tessar or Planar Carl Zeiss lenses. Excellent pics.
Mamiya 6X7: Japanese, 6X7, rotating back, larger negative, heavier, interchangeable lenses, fool-proof, magnifecent pics. I love both of mine.