When to Go
Temperatures in Buenos Aires Province rarely reach extremes. Note that some hotels and restaurants in areas popular with local tourists open only on weekends outside of peak season—this coincides with school holidays in summer (January and February), winter (July), and the Easter weekend. You'll get great discounts at those that open midweek in winter.
Early November's a good time to visit San Antonio de Areco, which holds its annual gaucho festival then. Like Buenos Aires, it feels curiously empty in January, when everyone decamps to the coast.
Though Iguazú Falls is thrilling year-round, seasonal rainfall and upstream Brazilian barrages (minidams) can affect the amount of water. If you visit between November and March, booking a hotel with air-conditioning and a swimming pool is as essential as taking mosquito repellent.