For L.A. by far KRTH has the best signal; I've been able to receive their signal as far north as Lompoc.
I recall KCBS-FM used to have a better signal, but that may be no fault of their own. In Santa Barbara 92.9 KJEE overpowers KCBS. Furthermore, if I am correct, doesn't KCBS have the highest tower?
In the Inland Empire I always thought KOLA had the best signal. It's one of the few, if only, IE stations which can be received in the San Fernando Valley. Oddly enough they're some areas in Ventura County where you can switch the antenna between KOLA and Santa Barbara's KTYD.
Interestingly enough I was able to pick up KYSR when I was in Ensenada, Mexico. This was the only L.A. station I was able to pick up that far south. It may of been possible with other stations had their signals not been overridden by local stations.
There is an area around Bishop where most of the Mt Wilson FMs come in.
In Big Bear most of the Las Vegas stations override the L.A. stations.
In Pasadena I've been able to receive, clear as a bell, Palm Springs' KDES 104.7.