Having visited the Iberia, Amex and AA lounges at EZE, I think I just ordered from best to worst (for EZE standards).

The Iberia one has the best food selections, and around noon when the BA flight to LHR departs, it's very quiet and almost empty, but it's even smaller than AA's.

The Amex's is divided in 3 areas, depending if you're a gold, platinum or Centurion cardholder. But the Platinum area is so small, it got very crowded very quickly so we decided to leave. The gold area was almost empty, and the seats looked more comfortable, though outdated. I don't have a Centurion card so I don't know how the respective area is.

And the AA's lounge is... well, you know.