Oh, boy. I've got a lot of favorites! XD
LAT - I love the design for all their models! The only thing I hate is that I can't use shaders on the face of these ones. XP
Mamama - I particularly like their Gumi model a lot! They have a very cute style.
Ohba Makoto - I don't particularly like their original models that much (they're a bit too sexualized for my taste), but they made my favorite LAT model edit, so... yeah. Also, they get bonus points for making beautiful hair physics. (Also, I forever hate that I missed the DL for the 13km edit for Sukone Tei and Miku. Cri. ;-;)
YYB - I like that everything in their style is very rounded and I very fond of the texture for their models!