It's all a matter of personal tastes and likes. Some people find skinny attractive and some don't. Also, what some consider "skinny" others would classify as medium.
I suppose the clothes look better on skinny models - maybe that's why designers prefer them skinny. I know for a fact (not because it's my personal preference :-) ) that most clothes look better on taller people, so if you want a tall model she has to be skinny - otherwise she'll look like a man.
Anyway - I like 'em thin, very thin...!
However I must admit that I'm not keeping up with current supermodels. There are too many freaky looking ones (I don't mean anorexic; their types of beauty are not what I consider attractive). I'm from the generation that was obsessed with Karen Mulder, Linda Evangelista, Claudia Schiffer, Nadia Auerman, etc. (I never liked Cindy Crawford even though she's from the same "batch").