Interesting. I have no experience with the Sigma, but with all of the others, several copies, plus the 50 F/2.5 CM, and several MF 50s, used with adapters.
Essentially, in my experience, with the exception of 1, the Meyer Domiplan 50 F/2.8, all slower 50s (F/1.7 and slower) are great lenses, usable from wide open, and very sharp from F/2, or from F/2.5 or F/2.8 if that is the maximum aperture.
When it comes to F/1.4s, it gets a little disappointing, as most 50 F/1.4s are soft wide open, don't focus too well at large apertures especially in close up circumstances, but they all get very good to excellent at F/2.8. This includes the "famous" Zeiss Planar T* 50 F/1.4, and the Canon 50 F/1.4. The best in this category, if you ask me, are the Sigma 50 F/1.4, followed by the old Zuiko OM 50 F/1.4, where the Sigma is sharper at F/1.4, and the Zuiko is excellent at F/2. Bokeh of the Sigma is a lot better.
However, IMO the best 50 currently out there, is the 50L. Slightly soft at F/1.2, sharp from F/1.4, and better than anything else up to F/2.8, and at least equal from F/2.8 and stopped down further. Bokeh, colour, contrast and flare resistance are all better, IMO, than anything else out there.
For some reason, all current fast 50s seem to have problems, however, generally related to focusing, so it is a matter of finding a good copy, or have the lens calibrated if it is not too far out.
My personal rating list of 50 mm AF lenses for Canon, both APS-C and FF is as follows:
1. EF 50L - just find one without the focus shift problem, in which case it is easily the best out there, there is no other lens which renders images this great. Slightly soft at F/1.2, and some halation around bright objects wide open (the glow people mention).
2. Sigma 50 F/1.4 - some copies with focusing problems nearby and/or far away, also some focus shift at F/1.6 to about F/2.5, and less sharp at F/2 and F/2.8 than at F/1.4 and F/4.
3. EF 50 F/2.5 CM - this is a gem: sharp throughout, and amazing bokeh. It is just relatively slow, and not very fast focusing, but it is one great little gem, often overlooked.
4. EF 50 F/1.8 Mk I / Mk II - usable at maximum aperture, sharp from F/2 to F/2.2, slow focusing at times. Sharpest at F/5.6 - F/8, pecular highlights are ugly due to the 5-bladed diaphragm.
10. EF 50 F/1.4 - I was really very disappointed by 4 out of 5 copies I tested, and just disappointed by 1 out of 5, due to focusing problems nearby, and the softness up to F/2.5; it only is really sharp from F/2.8, but then it suddenly is exceptionally sharp. Sharpest at F/4 - F/5.6
I have no experience with the Sigma 50 Macro.
If I had to add the Zuiko 50 F/1.4, not taking the MF into account, I would probably put it ex aequo with the 50 CM, although its bokeh is not as good. All other slow MF 50s are as good as the Canon 50 F/1.8s, and some are even better.
I have no experience with any of the F/1.2 MF 50s out there, like the Minolta, Olympus, Pentax or Nikon, so can't comment on those.
Kind regards, Wim