Best theatre in San Francisco?

I'm not sure if you meant live theaters or movie theaters. For live, I am a big fan fo the ACT--also the best acting company in my opinion as well. The Geary is great.

As far as movie theaters go there are number of really great ones. From classic old time theaters like the one in the Castro, to cool off beat ones like the Kabuki, to state of art theaters with a sleek look, like the one in the Embarcadero Mall.

Also, if there is the Foreign Cinema which is an restaurant that plays films against the wall while you eat--you won't really be able to pay attention to the film but it is kind of a fun experience.