That's a good question, and not so easy to answer. Naturally, you'd expect to find the sunniest beaches in Southern California, but I didn't want to make a guess (educated or not!) so I looked up a few statistics.
Unfortunately, the data was spotty, but what I found confirmed my guess that San Diego and Santa Barbara would be top picks. However, I was surprised to find that Santa Barbara (177 sunny days) turned out to be even sunnier than San Diego (146 sunny days), possibly due to their their lovely south facing beaches. Long Beach was also a surprise, being sunnier (with 159 sunny days) and warmer than San Diego.
But the real shocker was San Francisco, which has more sunny days (160) than San Diego. However, I believe the San Francisco data was collected at the airport, which is on the bay side and considerably warmer and sunnier than the coastal beaches. Believe me, the beaches along the San Francisco coast are not that sunny.
Of course, you also have to factor in the fog, which you'll find along the entire coast. In Southern California it mainly occurs in the summer. The locals call it "May Gray" or "June Gloom," and they really enjoy whining about it. But the fog usually burns off by noon, so you still have a long, sunny afternoon to enjoy the beach.
Here's what Wikipedia has to say about June Gloom
In Southern California, the number of days in May and June that are "gloomy" vary from year to year. Years with warmer ocean temperatures, referred to as El Niño, may result in fewer gray days in May and June. Cooler ocean temperatures, associated with La Niña, usually foretell a more gray period. Sometimes the cloudiness continues into July, a condition known as "Summer Bummer."
The figures for sunny days I cited don't include partly sunny days. If you add those in, here's the breakdown:
- San Francisco -- 260 days
- Santa Barbara -- 285 days
- Long Beach -- 278 days
- San Diego -- 263 days