The easiest way is the Buquebus (the boat-only option - there are also boat plus bus options - which only make sense if you also want to stop in Colonia). It is 3 hours from city center to city center. You can also fly AEP/MVD (which I've never done) - it probably takes a similar total amount of elapsed time - AEP is convenient to the city center so you won't need to deal with going back out to EZE. The boat ride isn't particularly scenic, but at least you can walk around a bit, there's a duty free shop onboard, marginal food and drink for purchase, etc. and overall, a more relaxed experience than dealing with airports.