Prime lens.

It's all well and good to say that people wouldn't be able to tell IQ of large EOS L zooms apart from prime lenses, but primes have the advantage that they are both smaller and cheaper than comparable zooms, and having a larger aperture helps with DOF.

For example while the new 12-35 certainly looks nice for slightly less money and around the same total size you could also get the Panasonic 14mm f2.5, 20mm f1.7 and the Olympus 45mm f1.8. The range is shifted a little towards the tele and it's not as convenient to change focal length, but you're getting a lot more aperture for your money and each lens mounted on the camera is much smaller individually.

It's really horses for courses, if you want focal length flexibility and don't mind a larger lens you can get the zoom, if you want large aperture and/or a smaller lens you can get one or more primes.