San Francisco is a city for the workout obsessed. We take our runs seriously, our Lululemon seriously and our gym classes VERY seriously. So what we want to know is this: who is the city's best gym class instructor?  We're talking across gyms and across classes (pilates, spin, yoga, bootcamp, cardio striptease - they're all fair game).  Whose class do you make sure you get on the waiting list for?  Let us know in the comments (plus the gym and the time of day they teach at). We'll do a feature on the most popular teacher.