Thanks for your reply.
I actually meant San Vincenzo. Typing while tired! We have found sea front apartments in both places - both tick nearly all our boxes, so it's which town has most to offer. 50 year old couple, like music (not dance music), informal restaurants, pretty views and towns. Any further thoughts appreciated.
The life style is quite similar. Castiglioncello was a VIP location in the past (many famous actors bought villas nearby). But now the most difference is the type of beach: Castiglioncello has a very short sandy beach (unless you don't move to Rosignano Solvay white sands), while San Vincenzo offers a very big sandy beach. In my opinion, panoramic views are more interesting near Castiglioncello (driving along the coast is lovely!), however the surroundings of San Vincenzo ( especially the Baratti Gulf and the ancient village of Populonia) are amazing too. You can find good restaurants in both places.
Where did you end up going to? Any notes or suggestions?