Just thought of another suggestion if you want somewhere quiet and that's Santo Tomas. Looked lovely when we visited for the day and the beach was not as crowded as Cala Galdana. Son Bou was lovely too, a vast expanse of sand and lovely clear sea. I think it depends on what you mean when you say quiet. We stayed in Cala'n Bosch this year, where there's plenty of choice for restaurants and a nice beach, but still not rowdy like some places. We visited Cala'n Forcat a couple of evenings as we had relatives who were staying there and I wasn't too keen...much preferred Cala'n Bosch. We also visited Arenal which was nice too, must have picked a bad day though because the sea was really rough, although my son thought it was great fun riding the waves. As Blanck mentioned watch out for the warning flags as jellyfish can be a problem, although after worrying about them prior to my holiday in August, we didn't see one at all in a fortnight.
To sum up, there's so many nice, quiet resorts in Menorca I don't think you can go far wrong. I think you need to consider the time of year you're going as that will obviously affect how quiet the resort will be, and whether you want a good choice of restaurants or will you be happy with just a few to choose from.
