The ergonomics of the Hasselblad allow me to shoot an entire roll without taking the camera with the prism finder mounted from my eye. I hold the camera in my left hand, release the shutter with my left index finger, focus and wind the camera with my right hand. With the focusing knob on the left side of the camera body rather than on the lens, I find focusing very clumsy with the twin lens Rolleis that I've used. I've never used an SL66, but the focusing knob is also on the left side of that camera.

If you're going to be doing a lot of hand held shooting such as for environmental portraits or weddings (does anybody shoot film at weddings anymore?) I'd recommend the 'blad. If you're going to do a lot of tripod mounted landscape or still life photography, I think I'd rather have the swings and tilts of the Rollei.

Unless you consider the Schneider lenses for the Rollei significantly superior to the Zeiss lenses used on both cameras, the lens quality consideration is really a wash.