I've tried most of them, and most were not good.
The best, in my opinion is Willy's in Agoura Hills, off the 101 freeway. It is generally in the LA area. They smoke all meats for up to 15 hours, and the smoker in the back is always going. Restaurant is up scale in decor, and friendly staff and owner.
It is five stars and most of the rest are 2 stars. But comparing them to places in Texas or KC , they would be 3 out of 5 stars.
Of course there is Texas Tyler Hogly Wogly, http://www.hoglywogly.com/, in Van Nuys( L. A.) Its been there for 50 years, and some people swear by them . I like them also. Decore hasn't changed in 50 years. But, bath rooms are like walking into an elegant french chateau.
Update- June 4, 2014-Willy's is now closed. And I forgot to mention that when ordering at Hogly, always ask for the meat to be dry( no house sauce) and not burnt( like in burnt ends). And Smoke City is better now.