I'll go so far as saying there are not any bad Leica OR Zeiss lenses made for the M - in fact no "bad" Voigtlander lenses either! The main difference is that the late model Leica and Zeiss lenses will maintain a ridiculously high degree of sharpness wide open, whereas the earlier ones will not be quite as sharp wide open (but certainly darn good compared to the general field of 35mm lenses). And yes the aspherically surfaced Leica's deliver that wee bit of extra performance for the most demanding among us (and wealthiest!).