Been through them all with the exception of the F's. The K55 f/1.8 stands out for me as the best value, most underrated, best portrait lens of the set. I never got on with the 1.7s, sharp for sure and more than capable of creating an image but you always had the feeling that the 1.4s were just that little bit more special. Hated the M's because they were smaller and built to some accountants spec, same with the A's but they at least had the extra functionality. The Super Takumar's and K's are sublime to use from a tactile sense and you know that they will still be going strong long after the M's and A's have fallen apart. Image wise, the 1.4s are smoother bokeh wise but it has to be said that there was improvements to the coatings over the years. The K55 renders colours a bit differently from the 50's, darker, richer, deeper and while capable of buttery smooth bokeh, stopped down a bit and it will get nervous.
The 1.2s stomp all over the others bokeh wise, but can suffer from halo effects with high contrast subjects. And you will need good eyes to focus using the viewfinder. If I personally was going to redo the list taking into account everything I've said I would put it this way:
A50 f/1.2
K50 f/1.2
F50 f/1.4
K50 f/1.4
SMC Tak 50 f/1.4
K55 f/1.8 / SMC Tak 55 f/1.8
F50 f/1.7
A50 f/1.4
A50 f/1.7
Non SMC Tak 50 f/1.4
Non SMC Tak 55 f/1.8
Then the M's
Whatever you get enjoy
To put this into real terms, I have the A50 f/1.2 and it resides in my bag with the 31, 43 and 77. A good friend has expressed interest in picking up photography and the first 3 lens that she does not yet know she has are the K35 f/3.5, K55 f/1.8 and a FA50 f/1.7 that I found for very reasonable money and I basically could not turn down