Salsa and Merengue are fairly popular in Buenos Aires. I'm sure you can check around on the internet and find some clubs. If you go to some of the young peoples' neighborhood clubs, you'll see people dance to Salsa, Rock and Tango. On the other hand, if you go to the real milongas, you might hear twenty seconds of Salsa as a cortina between sets of Tango. The cortina is a way of giving people a break to have a drink, look for new partners, use the restroom, anything but dance. That would only disappoint you quite a bit.
By the way, Buenos Aires is a city of about eight million. There is almost every dance there. Flamenco is fairly popular, too. One of the first people to actually stage Flamenco was an Argentine girl. People love Swing in Argentina, too.