Ailsa, I have used both the Mamiya 330f and Rollei TLR's. From the point of view of getting the job done (i.e. just taking good pictures), the simplicity of the Rollei's is hard to beat. Keeping it simple has an interesting side effect: you forget the camera and concentrate on the photography.
My best pictures have been taken with my old Rolleicord III (and I own a rather wide range of equipment: Mamiya 7II, Horseman VHR, Crown Graphic, several folders). Recently I succumbed to the siren call of a Rolleicord Vb (and it had grey leatherette finish, which was the clincher), but it's really nothing more than a fancy III! You can pick up a 'cord III for less than $200, get it CLA'd, and you'll have a real photographic machine to work with.
It's hard to transmit one's experience to others, and it doesn't always transfer over well, but here goes ... you can't go wrong with a Rollei TLR, and the simpler the better!