Im going to have to go with the 24-70 2.8 L, it is an extremely versatile lens, very good in low light as well. I have both versions, but I havent shot with the v2 enough to know if there are any inconsistencies or issues. One thing I am worried about with it is the color seems a little off sometimes. Need to do a head to head test.
70-200 2.8 L II is a close second.
16-35 2.8 L II is third.
As a wedding photographer those three lenses were enough for me to cover any event.
Well, my favorite lens and my most used lens are two different things. I would say that my workhorse lens is the 24-105 f4 L IS. It has a great, I love the constant aperture, and the IS helps me out tremendously for documentary and handheld work (keep in mind, I'm coming from a video background here). It probably lives on my C300 50% of the time.
My absolute favorite lens, though, right now has to be the 85mm f1.2 L. Good lord is that a beautiful lens. I get positively giddy every time I get to put in on the C300.
24mm f1.4 L is a close second.
It depends on what I am shooting but as a freelance sports photographer my 70-200mm f2.8 L is my workhorse and spends most of the time on my camera. I bought a 35mm f2.8 TS-E with an FD mount and converted it to the EF mount and use it for most everything else I shoot unless I need auto focus and then it's my 24-70 f2.8 L. As for a favorite I must say it's the converted FD Tilt-Shift. The lens is so versatile, sharp and down right fun to use.
Easy. 100mm f/2.8L Macro IS. I like photography in general, but macro is what I enjoy most, and spend a lot of time doing. This lens is one of the best out there for that, but is also fine for portraits and general use. A little long for a "walk around," on a crop, it'll be interesting to see what I can do with it on a FF (hopefully soon).