Chile is a long, narrow country, which means the right transportation choice changes a lot depending on how far you're traveling. Understanding this before building your itinerary saves you from losing entire days to transfers that could have been solved with a couple of hours in the air.
Long-distance buses
Within the same region -say, moving between cities in central Chile or within Araucanía- the bus is comfortable, frequent, and considerably cheaper than flying. Chile's long-distance buses tend to have a good standard, with reclining semi-cama seats on most main routes.
When flying makes sense
For trips between macro-zones -say, Santiago to Punta Arenas (Patagonia) or Santiago to Easter Island- flying is practically the only reasonable option: the same trip by bus can take more than 30 hours. Booking domestic flights ahead, especially to Patagonia in high season, helps secure better fares.
Passenger trains in Chile are far more limited than in other countries in the region: they're basically reduced to some commuter services in central Chile -there's no long-distance rail network between regions the way there is with buses or flights.
