Argentina is a huge country, so the climate varies from region to region. To the northeast, the climate is sub-tropical, whilst the central region is humid and the south the coldest. The best time to visit the country is between March and April and October/November; it's best to avoid the glacial cold that can affect the south, the heatwaves that hit the north and the rainy season. The lovely Buenos Aires is best visited during the Argentinian Spring, which is during the European Autumn, as the weather is pleasant. If you're planning to hike in Patagonia, any time of year will do!