Pluna flights from AEP are much more convenient than AA from EZE... by the time you count extra time to get to EZE (35-45 minutes versus at most 15-20 minutes), longer check-in times (international airport timing versus domestic/regional airport timing), more queueing (security, immigration), and I even think higher airport taxes... the experience from EZE can feel a bit as though you've wasted the time it might have taken to go by ferry on the ground.

I've done both and I would (and have) repeated the Pluna flights. As for the EZE flights, I got sucked in once by an $89 r/t on UA, only to feel that it was a huge amount of time being "processed" and when I saw that airport taxes (paid at the airport in those times) might have been $30-40 more roundtrip, the "savings" of the low fare were quickly erased.