For me there are numerous magic lenses, some I own, some I've owned (ouch).
The LM Hexanon 60/1.2 is scary sharp and contrasty from at least f-2.0 on down to ~ f-8.0. It doesn't suck at f-1.4 and really isn't bad wide open if the photographer does his part and gets it in focus. DoF for F-1.2 on a 60mm lens at 0.8m is less than that for f-1.0 for a 50mm lens at 1.0m, the magnification is somewhat more, too.
The Micro-Nikkor 50/2.8 AIS has always made me wonder can it possibly get any better? Granted it is only f-2.8 but it is really good at all apertures, well f-22, etc does present the potential for diffusion.
It is my belief that it is the individual image that tells the tale of the tape. Would anyone shoot a woman's portrait with a 75 Summicron if an older 90 Elmar with questionable coatings was available? Or a man's portrait with hard side light with a 50 Summilux (pre-asph) if any 50 Summicron was available?
Use the best tool for the job at hand with what you have in your tool chest. If you need your 50 Summilux pre-asph scary sharp use it at f-5.6 and don't point it towards any light source. If your 75 Summicron is too sharp then put on an old UV filter with a smudge of vaseline or take sand paper to it (the filter, not the lens) and create some diffusion.
Make the best of what you have. Realize there is no one best lens. In the hands of one who knows light and lenses much is possible.
If the image is good enough no one will ever ask what lens was used, save for maybe a member of some www forum.
