Buenos Aires is a busy urban city, not a beach city like Rio, and many locals, particularly those of the gay community choose their summer months to leave the city on Vacation. Where do a lot of them go? Rio!
Especially during New Years and Carnival, Rio is incredibly popular. In the hottest months, Rio feels like a large beach town. It is sultry and sexy, and while Rio also has great fashion, you'll find that most people will be wearing very little. In Casual but nice restaurants, people may be sitting around you wearing nothing more than bikinis.