I've always loved Corona del Mar, in Orange County, California. I haven't been there in a long time but it's always been a great place for a family day-trip.
Then there's San Felipe, in Mexico. It's on the western shore of the Gulf of California. I spent a week there when I was a teenager, camped out near a cliff overlooking the beach. Clearest, calmest, warmest water I've ever plunged into.
I visit the beach as often as I can but I can't remember the last time I took a swim or tried to work up a suntan there. That's because I'm afraid a bully will kick sand in my face, and steal my girlfriend or whatever. (I'm a 135-pound weakling). Mostly I'm interested in exploring the restaurants, taverns, shops, and sights along the shore. That's a really cool way to spend the day.