I shoot with Leica, Zeiss, Nikon, Fuji, Panasonic, Takumar, and Vivitar lenses. I periodically perform comparative image tests on these lenses. In general, all these lenses are capable of producing high-quality images. Here are some of the results that surprised me:
50mm f/1.4 8-element Takumar lens superior to my 50mm f/1.4 Nikkor
135mm f/2 Zeiss superior to my 135mm f/2 Nikkor
28mm f/2.8 Nikkor equal to my 28mm f/2 Zeiss
35mm f/1.4 Zeiss, 35mm f/1.4 Nikkor, 23mm f/1.4 Fujinon very similar in performance
21mm f/1.4 Leica and 21mm f/2.8 Zeiss very similar in performance
28mm f/2.8 Vivitar performed slightly better than my 28mm f/2.8 Takumar
105mm f/2.8 Takumar equal to 105mm f/2.5 Nikkor
21mm Lens Test by
Narsuitus, on Flickr