Limited knowledge of wider France but can rule out Nice as the beach is pebbles - like Brighton. Nice does however have wall to wall restaurants, most very good quality and of average expense. There's a casino, plenty of nightlife and good rail/bus links with places west (St Tropez and Cannes) and east (M. Carlo and Monaco). Can even get ferries from Nice to Corsica for a 2 day trip.

Should say that whilst the beaches are pebbles there's perhaps a dozen "private beach areas" where you rent a very comfortable, padded lounger for the day complete with umbrella. These charge about 12 euros each per day so it can be expensive if you do that every day but we usually indulge 2-3 times a week. They even have restaurants 20 yards back from the loungers, still in the "private" area and their choice, quality and prices are excellent.

Beware of Juan les Pins also on the Riviera (west of Nice) as accommodation is generally set well back from the beach (which is OK) and is accessed via underpasses beneath the coastal main rail line. Stayed here once, didn't enjoy and moved on earlier than expected.

Hope this helps a little.
Mike