It depends on what you use as your starting point. The earliest airliners (e.g. the DeHaviland Dragonfly or the Boeing 247) were cramped, noisy, and loud. Things get better in the 1940s and 1950s as newer aircraft like the Lockheed Constellation come along. Bigger aircraft mean more room for passengers and faster aircraft mean shorter flight times over longer distances.

The jet age really shakes things up. Airlines like PanAm cater to the "jet set" of upper- and middle-class people who can afford air travel (at that point air travel was affordable, but still fairly expensive). One of the major selling points airlines try to pitch to would-be passengers is the comfort and luxury of air travel. Attractive stewardesses, free drinks, even in-flight movies. Now, 707s and DC8s aren't especially big aircraft, so space is still limited.

The Airline Deregulation Act in 1978 changes things up a bit. Airlines charge lower prices and start to compete more and more on price. Ticket prices drop and airlines work on cramming more and more people on each flight.

Also important for the post-war rise of commercial aviation were the hundreds of thousands of trained military pilots being thrown back into the work force.