Tregantle at Whitsand Bay. I walk there several times a week and it’s my absolute favourite in Cornwall. South coast so it’s warmer, miles of golden sand, peaceful, and some interesting pieces of shipwreck to be found.
If I was a holidaymaker / tourist though I’d probably go for one of the beaches mentioned above. There are no facilities at Whitsand Bay and you really need to know your tides to be safe.