I was going through a similar decision making process about 18 months ago. Three lenses were on my radar, as firs thte 7D and then the 5D MkII when I got it were showing up the deficiencies of my 24-105 at 24mm. Initially, there wasn't really anything better enough to pay out silly money for, as the original EF 24mm f/1.4 had it's own problems, but then over a relatively short period, the EF 24 f/1.4 MkII, Zeiss 21 and T/SE 24 all appeared and all came out well in reviews. At the time, I was looking for a landscape lens (so manual focus) in that sort of range and was leaning towards the Zeiss, based on reviews and real life sample images (although very few exist for the tilt shift). However, recently, I arranged a northern lights trip, so a fast lens was more important than when I was originally deciding and that pretty much decided it. The reviews put the Zeiss and the f/1.4 even in terms of image quality, but one review stated that the Zeiss had that indefinable something, a certain look the Canon lens couldn't match. I would therefore say, if you might need a fast aperture, then don't rule out the Canon, but if you are only ever going to be using narrower apertures, then I would lean towards the Zeiss. 3mm can be important at wide angle and you can always crop or move if the 24mm field of view is important compositionally, so you have a bit more flexibility, then there is the difference in contrast. Ultimately, the test is going to be a trial though, as I'm sure some would prefer the look of the Zeiss and others the look of the 24 f/1.4. Also for seascapes, the ability to use a wider aperture to capture more wave definition and movement and still have sufficient DoF might make the tilt and shift a better proposition.
