I also vote for Hapuna Beach on the Big Island, especially when you can have fish tacos for lunch from the snack shack there.

OK - how about the best secluded beaches - where practically no one else is in sight?

Makalawena on the Big Island is secluded (about a fifteen minute walk from the nearest parking), and has three crescent beaches separated by lava outcrops, with powdery white sand, large sand dunes behind the beach, sparkling turquoise water, and great swimming and snorkeling.

The best secluded beach is past telephone pole #71 just past Kohala on BI-incredible!!!!!