Tastes differ - I personally felt Din Tai Fung here in LA was just OK and not worth the wait (but i never tried other locations).
While i can't say about "the best" in LA a great bet is a trio of places side by side in a plaza in San Gabriel next to Hilton. We usually go to MeiLong Village (as they pack some frozen stuff on ice for us to take home) but the other two are just as good.
1. J & J / Jin Jian Restaurant
301 W Valley Blvd
San Gabriel, CA 91776
2. Mei Long Village
301 W Valley Blvd
San Gabriel, CA 91776
(626) 284-4769
3. Happy Kitchen
301 W Valley Blvd
San Gabriel, CA 91776
(626) 284-2619