Take a bus from Buenos Aires to Neuquen, then rent a car in Neuquen and drive to the mountains. You can easily make a roundtrip from Neuquen thru Alumine, San Martin, and Bariloche, and that makes a great trip. The road through Zapala is incredible. Neuquen itself didn’t see very interesting, though it’s okay for an afternoon. Rather stay an hour or so out of Neuquen at the hotel on the lake in Villa El Chocon, where there are some interesting dinosaur footprints.