I have been to the following beaches in the u.s;
Florida
Panama city beach
Pensacola beach
Fort Walton beach
Mexico beach
Port Saint Joe
Daytona beach
Ormond beach
Flagler beach
Alabama
Orange Beach
Georgia
Savannah/Tybee island
Jekyll island
North Carolina
Wrightsville beach
The best ones in Florida (to me) were mexico beach/port Saint Joe, there is not a lot of people or touristie crap there just nice beaches with reasonable accommodations. The other Florida beach I really liked was Flagler, I don't remember a whole lot about it other than we camped there several times and you could walk from the campground to the ocean no problem and it wasn't very crowded either
Same with orange Beach in Alabama, it's in a mostly residential area and not crowded or touristie at all, I went to do the battleship/ submarine tour in mobile and wound up at the beach afterwards.
Wrightsville beach in north Carolina has to be my second favorite, it too is nestled in a mostly residential area but there are a few excellent restaurants tucked away here and there and the blockade runner is an excellent hotel. This was another accidental find when I was touring the battleship in nearby Wilmington. Would 100% recommend and will go back.
My absolute favorite has to be Tybee island, there just isn't a lot there and the beach seems to go on forever, it can get a bit crowded down around the boardwalk and hotel Tybee area but down by the lighthouse there is nothing but beach and water and you can watch the huge container ships glide in and out of the savannah river. And if the weather won't cooperate for a beach day there is plenty to do in nearby savannah, a very old town very rich with early American history I recommend the maritime museum it's a cheap and fun thing to do and if you get thirsty you can run across town to the pirate house (oldest building in GA supposedly) and order up the captains artillery... Just don't try the historical stairs across bay street afterwards!