Owned both and passed them on. My RB was a nice camera with the rotating back, but just as heavy as my 4x5. Add the metering prism and with a couple of lenses it's just as bulky as a 4x5 outfit with a handful of holders. For out and about shooting it suits tall people with big hands better. Rack out the bellows any and you'll have to comp the exposure according to the side mounted scale at the bellows without the metering prism.
I had a 501CM Hassy with a 60Cf and it was front heavy. All that great glass is weighty. Extra lenses are the expensive part. It went. Screen wasn't as good as my 6006 Rollei and lenses are generally comparable between the two. A 6008 body with grip would be a better choice but again lenses are the expensive part, especially the Schneider's for the Rollei.
In medium format having held or shot a few different one's I like the Fuji 6x7 and 6x9's. Great cameras. Mamiya makes the great 6x7 with stellar lenses, but the 6x6 is getting long in the tooth.
In the end I wouldn't buy either. I've looked at Hassy again and again thinking just a kit with a 80 might work but to tell the truth it's a boring setup. Better off with a PII Pentax.