I would personally recommend Hawkins Cheung.

As far as I'm concerned nobody really teaches the structure aspect like he does... he is a very small guy, and I take it if he was to use Wing Chun effectively it must be technically perfect, or as technical as possible.

One of my friends used to train with Hawkins, and he a lot of good things to say about him. His student, Jin Young, teaches in the Century City area.