You don't mention Primary use, so I'll assume Landscape/Buildings.
I own & use both Primes & Zooms in the 8-24 range (Canon 8-15f/4, Canon 16-35f/2.8, Canon 24f/1.4, Zeiss 15f/2.8, Zeiss 21f/2.8, TSE 17 II & TSE 24 II.
For general walk around the zooms work just fine, have some issues with purple fringing & CA on the 16-35 but can mostly be fixed in post.
For dedicated time no issue Landscape work, the Zeiss 15 & 21 are superb, better than anything Canon can offer with the exception of the TSE lenses, but, your stuck with Manual Focus, with Live View I don't find this an issue.
For anything that includes Buildings, the TSE lenses are the way to go, I use them where I want DOF throughout the Image front to back.
If I was to select just the one best Lens for all round excellence, the Zeiss 21f/2.8, I use this on the 5DMK III, the 1Dx & now the Sony a7r, great piece of Kit.