If you're cutting through shell or bone, double bevels have a more durable edge that can handle a fair bit of abuse. They're cleaverlike. I don't think they're very good for chicken unless you're going through bone (in which case, they're great). Single bevels are slightly better at removing filets because of the geometry, but I think the difference between a traditional deba and a western deba in this respect is often exaggerated. Technique matters more than bevel type for cleanly separating flesh from bone.
In my experience, sujis and yanagis are basically equally good at taking skin off a filet.
In my experience, sujis and yanagis are basically equally good at taking skin off a filet.