Hi, David! I think it's going to boil down to which focal length will work better for the types of shooting you have in mind. The 14L II is REALLY wide on a FF. A friend of mine has the 20mm Voigtlander on his 5D II and feels even that is too wide for the landscape shooting he likes to do. I recently picked up the Zeiss 21mm and haven't done a lot of shooting with it yet except for test shots. The Zeiss does appear to have a different look than the Canon lenses, bringing out more subtle details. The MF of the Zeiss lens hasn't really been a problem since you get the focus confirmation. When I tested the lens to see if it needed any microadjustment, it was spot on at the zero setting.
Cameras: 1DX, 1D4, 20D, 10D, S90, G2
Lenses: Canon 10-22mm, 16-35mm f2.8L II, 24-70mm f2.8L, 70-200mm f2.8L IS, 300mm f2.8L IS, 200mm f2L IS, 50mm f1.4, 50mm f1.2L, 85mm f1.2L, 1.4x TC, 2x TC, 500D macro, Zeiss 21mm
Lighting: 580EX, Elinchrom 600 RX's, D-Lite 4's, ABR800, 74" Eli Octa, 100cm/70cm DOs, Photoflex Medium Octa and reflectors, PW's, Lastolite Hilite, Newton Di400CR bracket