Excellent advice and information as posted above. I agree 200% that you should try to make one of the big Copa Libertadores games, as they involve River Plate or Boca Juniors - which are two of the largest and most popular Teams in all of South America. The Libertadores tournament is the South American equivalent of the Champions League in Europe, so you can expect Stadiums to be 100% full. As noted, ticket prices will be expensive. For visitors, I suggest going through one of the reputable travel agencies that offer a turn-key solution, which should include Hotel to Stadium transportation (both ways).