QUOTE(maratial @ Nov 30 2010, 03:24 PM)
In early January will not find any quiet beach, because it is full holiday season and everyone travels to the beach.
Punta del Este and Punta del Diablo Uruguay's beaches are not in Argentina. I do not recommend anything at all go to Mar del Plata and Pinamar since they are full of tourists. Rosario has beaches on the Rio Parana, but also saturated with vacationers.
In any case it is preferable to choose a slightly smaller beaches and family as Tuy˙ San Clemente, Santa Teresita and Mar de Ajo, where although there will be people will be less than the other places you listed.
Thanks for everyone's feedback - I am back now from my trip away, and in the end we decided to go to La Paloma (mainly based on accomodation options in jan, and proximity to BA). This was a great compromise as quiet a small town, but lots to do in the evenings, and there were 3 beaches to choose from:
- a small quieter beach near the lighthouse
- long, sandy beach which was better for swimming and families
- long sandy beach with big waves, which was more lively.
We had a combination of all 3, depending on time of day - the lively beach was great for the afternoon/evening, where the younger crowd went, and where there were a couple of bars.
Hope thats helpful to someone else in the future!