If the goal is to simply maintain the status of having a "super sonic" air force and nothing else, the F1s make perfect sense. For a few hundred million dollars you get 20 planes, all the tooling, manuals and supplements that the Spanish Air force has and you are done. If you buy MIGs and Chinese fighters, you have to pay for the price of the planes plus extra for the maintenance contract, completely new tools and supplements that are entirely different from the western standards that Argentina has used so far. So, it is much more expensive.
I don't think the ultimate goal is to have a truly combat capable air force. The goal is to simply maintain some type of status. Remember that Argentina was the first country in Latin America to have combat jets and to have super sonic planes. But the MIRAGE III, which were the first super sonic planes used south of the Rio Grande, are just too old to fly. If they are retired without replacement, Argentina's air force will be at the same technological level as the Paraguayan or Bolivian air forces, which for some is unacceptable. So, to maintain an illusion of progress, you buy a bunch of old F1s from Spain which can be used to fly during national dates and that is it.
Fianlly, after the NSA scandal, I very much doubt Brazil will buy the F-18E Super Hornet, which used to be a certain deal. The race now is between the French Rafale and the Swedish Gripen NG.