That really depends, do you shoot a lot of video? Zeiss lenses are definitely the better choice for video, the focus ring is butter smooth and has much more throw than L lenses. Also it has hard stops, if you put focus marks on an L lens and accidentally spin past infinity, the focus marks become useless. They are built like tanks, all metal and even the lens hoods are metal.
I've had tons of L lenses and still have a good many, but I was blown away by the Zeiss glass. Particularly the 21mm f/2.8, the 100mm f/2 Makro, and the 50mm f/2 Makro. They are so sharp edge to edge it's unbelievable. Even the 35 f/2 (one of their cheaper lenses) is as sharp as my 35L. I would say that their Canon counterparts are equally sharp in the center, but the Zeiss glass is killing it in terms of edge sharpness. Also they have very very uniform color across the board, so matching color between shots is very easy. They definitely have a unique look, very contrasty but with incredibly fine detail. If you hit the sweet spot on those lenses they separate the subject from the background like no other, creating almost a 3D effect (here is an example, not the best, but the first I could find)(100mm Makro):
I have been trying to make myself get rid of all my L lenses and replace them with Zeiss glass, but can't bring myself to let them go, but I think I'm almost there. The thing about my 1.2 and 1.4 primes, I rarely shoot video below f/2, and the Zeiss glass retains sharpness well even stopped down, so I can live without the extra stops. Sure they don't have AF, but that just means more money going to optics.
I think the only Canon lens I'll end up keeping is my 14L II, as Zeiss doesn't make anything ultra wide ZE mount lenses at the moment. But if the 15mm f/2.8 rumor comes true, I may have to give up the 14L as well.