Depends on the area... Cinque Terre are beautiful. They are: Monterosso, Vernazza, Corniglia, Manarola, Riomaggiore. Portofino is beautiful, too.
I don't like Genova. I suggest only its aquarium. It isn't a great place for beaches and sea.
I prefer Tuscany or Riviera Romagnola (Emilia-Romagna).
In Tuscany, you could choose a place near the see and near some great cities. So you can stay to the seaside and have some daily trip (going by train) in Pisa, Siena ect.
However, as for Romagna, you could go in Rimini, Milano Marittima...