Where can I buy the best loose tea in LA Chinatiown?
Definitely check out the links Servorg posted, as well as some other threads about tea on the LA board. Note that Tea Habitat's brick and mortar is now closed (though they still sell online). Bana Tea (http://banateacompany.com/) is also online-only, though the owner does do presentations and public events occasionally. Valley Coffee in Tea has some OK stuff if you're into their particular style of tea, however, you generally can't try the teas in person, and they won't sell less than 4 oz (at which point, you might as well buy online). Wing Hop Fung (both Chinatown and SGV locations, as well as Bird Pick locations around Southern California) will allow you to try; there are a few gems there, but I think overall, the tea quality / value is just Ok.
While there's some obvious benefits to be able to try tea in person before buying, I would really suggest trying some online merchants vs. any of the places in Chinatown (or the SGV for that matter, though SGV overall will be better than Chinatown for tea shopping).