Owned both brands over the years. Agree with what's been said so far. Both are neutral speakers, but the Kef more so. Dynaudio has a slightly more forward and robust/rich/soft presentation, Kef slightly more laid-back and open.
The Kef lets you see deeper into the recording, but at the same time will also highlight any deficiencies in your front end components and is less forgiving to poorly recorded program material. I think the more forgiving nature of Dynaudio makes it cheaper and easier to achieve good sound with a modest front end, whereas Kef will reward you more with better components. Both speakers require high power to sound their best, in my experience.