One question that Canon EOS users might be asking themselves is whether to go for the Canon 24/1.4L II or the Zeiss ZE 21/2.8 Distagon. The ZE 21/2.8 is easily the standout in the wide angle Zeiss ZF/ZE line, especially for Canon users. The most-similar Canon alternative is the 24/1.4L II (reviewed in DAP).
A 24mm f/1.4 offers low-light versatility, but 21mm offers distinctly wider coverage than 24mm. Both lenses are superb, both have idiosyncrasies, yet I have little hesitation about either. A distinction of note is that the 21/2.8 Distagon is a flat field lens, whereas the Canon 24/1.4L II has a curved field (wavy), which requires stopping down for some subjects, as well as awareness of its behavior. I don’t see them as competing except in a glancing way. In terms of build quality, the Zeiss 21/2.8 is pure elegance, but that is immaterial to optical performance and should not be the top consideration for making images.
To oversimplify, get the Canon 24/1.4L II for all around handheld shooting, especially indoors, or anywhere you might need fast speed and autofocus (eg crowds and people, fast-moving subjects). I see the Zeiss 21/2.8 Distagon as more of a landscape lens, and one where wider coverage is needed. But ironically, I also see it as more appropriate for night shooting because of its reliable flat-field excellence wide open at f/2.8 (a page of night examples is presented in my review). I also greatly prefer manual focus feel for close-up shooting (a page of macro examples is presented in my review).
Autofocus might really matter for some shooters. While the “green dot” focus confirmation works well with the Zeiss 21/2.8, anyone with less than 20/20 vision should stick to autofocus, eg the Canon 24/1.4L II.