http://www.tiendaleon.com.ar/home/home.asp

This is the website for the major provider of airport transfers to both the center of the city and between airports. You Can by ticket with credit card as you exit customs before you get to the public area. With 2 or 3 persons I would get a cab from them . 40 peso each for bus and 141 peso for a cab . The bus stops in the city center first so a cab would be quicker.