I enjoy visiting Jack Mond and trust it much more than any of the others in L.A., but after 4 visits have still not bought anything there. Not really their fault, just lack of inventory on what I was searching for at the time. If you are looking for a 321 Speedmaster, there are usually only 1 or 2 in house at the moment, since I think that is the thing most people are looking for from him. (I seem to remember a lot of 321 Seamasters, though.) Fun place, though, and a must-visit for Omega nerds.
Jackmond is located in Beverly Hills on Canon Dr. Just north of Wilshire Bl. Worth a stop just to see his collection.