Kernuak said:
I'd be interested in hearing from anyone who is used to using both and has made a direct real world comparison for similar scenes. That said, the results are probably just as meaningless, as I needed a wide aperture for shooting the northern lights, which is the reason I went for the f/1.4 over the TS/E and Zeiss 21mm, otherwise it would have been a hard choice to choose between the three.
I have both the TS-E and 24L II. The TS-E is sharp in the corners at f/3.5, but truthfully, I rarely shoot at any aperture other than f/8. In comparison, I generally only use the 24L II at f/1.4 to f/2.8. At f/1.4, it is fairly soft. At f/2 to f/2.8, it sharpens a lot. I have not compared their relative sharpness at the same apertures.
I look at the two lenses as having very different purposes in my bag. To my eye, the TS-E appears to be my sharpest lens. It is my favorite landscape lens (followed by the TS-E 17) because the tilt offers edge-to-edge sharpness and the shift straightens walls and provides for shift panos. The 24L II is perfectly suited for the Northern (or Southern) Lights or anytime that you need a sharp, wide, fast lens with AF. For the Northern Lights, I would only use the 24L II. It would also double as an excellent landscape lens. Of the two, the 24L II is more flexible and more usable as a walk around lens.
I cannot speak to the Zeiss 21mm. For my shooting, I would prefer the 24L II over it because of the AF, which I find very helpful.