Rollei never really made an "unpro" camera model. For durability and longevity I think the Rolleiflexes are on top, however with less moving parts, bells and whistles the Rolleicord seems for me the most stable and robust camera. They were considered as consumer models but when compared to the Flexes almost identical.

However, I heard after the 1970's Rollei started to build in plastic parts into their cameras. So maybe the pre 1970 models, during the hey days of TLR's are considered the best cameras.