Will you have a rental vehicle?
I like Huntington Beach for the true beach feel.
https://www.surfcityusa.com/
Long Beach is fairly close, this is more a tourist location, with the Aquarium of the Pacific, the Queen Mary, boat excursions and more.
http://www.visitlongbeach.com/
The closest would be the Balboa Pier area of Newport Beach.
http://www.visitnewportbeach.com/vacations/balboa-peninsula/
So just playing in the sand and ocean, I would look at Balboa Beach first, then Huntington Beach.
If you are looking for more off-beach activities such as walking up and down the boardwalk (fancy concrete sidewalk) and renting vehicles, I would head to Huntington Beach first, followed by Balboa Beach.
If you are looking for an overall day of activities and things to do, including some time on the beach, I would head to Long Beach and maybe a stop as Seal Beach next door.
Now without a car, you have some issues.
Balboa Beach is reachable by public bus (basically OCTA Route 43 south down Harbor and transfer to Route 71). Takes close to 2 hours each way.
Another choice, take the Metrolink Train/Amtrak from the Anaheim area to the San Clemente Pier, the train station is right on the beach.
Hope that helps.
Let me add the Orange County coastline and my preferences..
1. Huntington Beach for its size, things to do and size/parking.
2. Long Beach for its variety. (Love the Belmont Shore area for the sand and shops)
3. Balboa Pier/Beach area of Newport Beach.
4. Seal Beach
5. Sunset Beach
6. Crystal Cove
7. San Clemente
8. Dana Point
9. Laguna Beach (don't like the small beaches, lack of parking, pain to drive to, and more)