Of the big three (four if you count Nikon's premier line) whose coatings best handle low light situations?
You'll probably get some opinions, but everyone is using pretty darn good coatings on high end stuff these days, and I suspect the differences are nothing to fret about. I'd be more concerned with the fit and feel in your hands. Which feels best to you?
Clear skies, Alan
ZEISS, ZEISS, and ZEISS.