There is no "best" single lens for a wedding. You need to have a variety of lenses that will cover different situations. A good combination (for Nikon) would be a 17-55 2.8, a 24-70 2.8 and, a 70-200VR 2.8. This is just a basic selection of lenses to cover most situations then you could use a variety of different specialty lenses like, a macro for ring shots, a 10.5 for ultra wide creative group and individual shots, mabye a lens-baby for creative focusing some shots. So as you can see there is no "best lens just a group of core lenses to get and expand on. Now to knock all this out for me when I started and for 3-4 years all I had was a bronica and a 75mm lens (75 bring the "normal" focal length for 645) so I guess you can get away with a high quality, what is "normal" for digital, 30mm.