Nice or Naples?

[NewTravellor]

Hello all! I will be travellign for the first time for 3 weeks in June with a friend and will be visiting London, and will be visiting LOndon, paris, amsterdam, interlaken, rome. We would like to squeeze in 1 more city, either Naples or Nice. We do not know enough about either one and would love some suggestions. We're also hoping to find a beach we can enjoy for a day and were wondering if we could do so in one of these areas. Which would be a more worthwhile city?

[BigRay]

Definitely Nice! ;D
(Although the beach in Nice has small stones and not sand, you can get sandy beaches in the smaller towns right next to Nice.)

[Cil]

If you had the time, you could take a day or so from Rome and take a beautiful trainride to the Amalfi, nice beaches there.