it's really tough sorting through vintage lenses, and the optical gains may not be that huge. I'll put in my 2c based on each focal length I've used, all on 36-42mp bodies.
24mm, tried FD and OM. I like the OM for much smaller size. Possibly better IQ goes to the OM, however contrast not as high as say an L prime. Tried to do a compare with the 24-70ii and stopped down, no noteworthy differences except for contrast, where canon has the edge. Good to excellent on a high MP body.
28mm FDn, not super optics, but decent. Probably pushes a lower res body to the limits, however leaves something to be desired on a high mp body. Edges not really pin sharp even stopped down.
35mm f2 FDn, about the same optics with the 28/ motor drive 35 f2.
40mm f1.4 voigtlander classic. similar optical performance, vignettes really hard, stop down far corners never really sharp, somewhat busy bokeh
50mm f1.8 FDn, see nifty fifty, similar performance.
50mm f1.4 FDn, see EF 50mm f1.4, similar performance.
50mm f1.2L FDn, see EF 50mm f1.2L, similar performance.
50mm f1.2 nikon, softer than the canon version wide open, but sharper stopped down.
50mm f0.95 mitakon, about sharp as the canon EF 50mm f1.2L, with even better bokeh. Large and heavy
85mm f1.2L FD, see EF 85mm f1.2L
105mm f2.5 AI-S nikon, wonderful portrait lens, nice bokeh, decently sharp wide open, while the very slight halo effect gives portraits a nice glow to them.
135mm f2.8 vivitar, 135mm f2.8 FDn, 135mm f2 FDn, all decent optics, CA wide open, decent to great bokeh, great wide open and stopped down.
200mm f2 Nikon, clearly not as sharp as the latest canon, but it's similar to the 105 nikon. It's pretty sharp wide open, probably on the level of the 135's, stopped down performance, I have no clue, it's literally taped wide open to prevent accidental bumps 
200mm f5 OM, decently sharp stopped down, very hard to control since it's so lightweight along with the focal length. Lowish contrast, love the size of the lens, so hard to part.
Sony A7siii/A7iv/ZV-1 - FE 24/1.4 - SY 24/2.8 - FE 35/2.8 - FE 50/1.8 - FE 85/1.8 - F 600/5.6 - CZ 100-300 - Tamron 17-28/2.8 - 28-75/2.8 - 28-200 RXD
Panasonic GH6 - Laowa 7.5/2 - PL 15/1.7 - P 42.5/1.8 - OM 75/1.8 - PL 10-25/1.7 - P 12-32 - P 14-140