Of the three San Clemente and San Mateo are the nicest. San Onofre is the worst CG we have ever stayed at, bysides being next to the freeway and train the trails to the beach are steep and the beach is very rocky. At San Mateo most of the sites have bushes between the sites so you have some privacy, it's a over a mile to the beach by the trail. For your first time camping in the area the best choice would be San Clemente. While you're there you can explore the area for future trips.
Chuck & Teri, 1999 35 ft. Dolphin 5350, F53 Chassis with tag axle, Chassis build date 1/99 in Mexico, Banks System, Trans Command, Air Lift Air Bags on rear, Koni Shocks, Blue OX TruCenter, TigerTrak track bars front and rear, Roadmaster 1-3/4" rear auxiliary sway bar, 2013 VW Passat TDI SEL Premium, 1994 36 ft. Avion 5th Wheel. FMCA #F430129