It sounds like an oxymoron, but it really was the most luxurious bus ride I'd ever experienced. And for a seventeen-hour bus ride, it was actually pretty enjoyable. We left Buenos Aires in the evening, enjoyed a pink sunset from the large and clear windows and were then served soda and a tray of snacks.
The idea of a server on a bus was nowhere in my consciousness, and it was such a nice surprise. We were even offered a box with chicken and rice, but we'd just eaten, not knowing we'd be served dinner on the bus.
We slept in comfortable reclining seats with foot rests equivalent to first-class seats on a plane (complete with blankets) and enjoyed seeing the Argentine countryside on our way to Tucumán.