Over a period of some 40 years I have used Rollei TLR's, Mamiya TLR's, Bronica, Hassleblad and Rollei SLR's. I got my first Rollei SL66 sometime in the early 1980's used if for around a year and traded it for a Hassleblad. The Hassie lasted a year or so and then I went back to the SL66 which has remained my 6x6 of choice since. It feels the best to me, has great flexability and great optics.
OTOH, 6x6 is the format I shoot least frequently in most instances; I shoot primarily LF. But there are some times when it is perfect. Two weeks ago I had to shoot a summer festival, antique car show, etc. The SL66 with a couple of lenses and backs did the eyoman work that day.