I’ve been using Incase neoprene laptop sleeves for the past 3 or 4 years.
I’m not sure why.
I wanted a sleeve that would enable me to recognize it amongst a pile of laptop cases. Just about every sleeve follows the same formula as Incase: form-fitting neoprene and a zipper. One of the few manufacturers making something different is ColcaSac (formerly AppleSac). What they make is basically the opposite of the Incase sleeve: natural materials, velco flap, and not formfitting.