I have eight 50's for my rangefinders and three 50's for my SLaarrrghs.
My RF 50's are:
Summilux-ASPH, Summarit (the old one), Summitar, two f3.5 Elmars (a black scale that needs a CLA and a red-scale), Jupiter-3 "Brianov", two Industar-22's (one is mintish - the other is garbage).
I've used the Summitar the most but I'm sure that is going to change because I just got a Summilux-ASPH. I really like the rendering of the Summitar very much and because it is collapsible, it makes for a compact camera whether it is mated to my IIIf or one of my M's.
My other 50's are a 50 f1.4 Super Multi Coated Takumar (the radioactive one), 50 f1.8 SMC-PM, and a 50 f4 CZJ Flektogon in Pentacon-6 mount. Yes technically 50 Flek is my wide-angle lens for my medium format kit but I have these Pentacon-6 to Pentax-K adapters that have tilt and shift functions. So I sometimes use the 50 Flek on the Pentax as a tilt or shift lens.