I think a 3.5 Rollei is the way to go -- lighter than the 2.8s but yields nothing in terms of image quality. But I agree with others' comments that the Yashicamat produces really excellent results. I do understand, though, if you want to go with one of the top shelf brands, and get one of the fancier lenses along the way.
Hasselblads are surprisingly lightweight and decently compact. But they're definitely heavier than a Rolleiflex, and not as compact. And they're much noisier (thwoop!).