I was back and fourth on the 24L and the Zeiss 35... In fact if a deal hadn't fallen through I would have purchased the 24L...
I feel like the 24-35mm focal length is an entirely different animal to the 21 and never really considered it (despite it's reputation). If my primary concern was landscapes, however, I'd pick it up over all of the others! For people pictures and general photography I feel the 24L or 35 is a better FL.
Someday, I plan on a 24L purchase... After I get rid of my 5D and pick up the mk2!
I do have the precision screen and the fact that the aperture and focus confirm still work really don't make this a difficult lens to work with. You can get a steal on the Distagon, I bought mine for $800, and sell it at no loss if you don't like the MF...