In an old brief case, I came across a map of Western Europe published by National Geographic in 1929. One of the plates published in the margin included a map of the passenger airline service as it existed at the time.

[Link to full map ~1MB]
I imagine that the Budapest –> Vienna flight must have featured a rather marvelous bevy of passengers… Most of the flights in Europe at this point were conducted in re-purposed WWI planes, with rather rough conditions that were, apparently, best endured for less than two hours at a stretch.
Commercial aviation in France was not a serious prospect until after World War I. Because of widespread damage to railroads all over Europe, air travel offered a convenient alternative means of transportation. The cross-channel route from London to Paris also offered a tempting opportunity for enterprising entrepreneurs. Near the end of the war, on February 8, 1919, a group of French businessmen had remodeled the Farman Company’s twin-engine Goliath biplane and began flying routes across the English Channel between Paris and London. By August 1919, Farman was offering daily service on this route for as many as 14 passengers. To attract passengers, the interior of the fuselage was arranged much like a railway coach. The early burgeoning private services, however, proved not to be financially viable because of high operating costs, high fares, and low passenger turnout. French commercial aviation, like aviation in Britain and Germany, would not have survived without strong support from the government.
The French government took an active role in fostering a domestic commercial aviation industry. French officials believed that aviation would be an important part of the country’s economic growth. They also believed that a strong air presence would extend French political and diplomatic influence to the new postwar world. Passenger comfort was not high on many of these services. As one aviation official noted in a report from 1922, “In some airplanes, the passenger cannot stand conditions for more than two hours.”
[US Centennial of Flight Historical Commission Essay]

Farman Goliath F 150 - Original Usage: Reconaissance / Bomber/ Torpedo-Bomber.
Potez 7, a commonly used passenger aircraft by the French airline Franco-Roumaine in the 1920s

The Ford Trimotor 5-AT, nicknamed “The Tin Goose,” was used by almost all the U.S. airlines. Introduced in 1928, these planes could carry 14 or 15 passengers in its corrugated fuselage. It was produced through 1932, but these planes stayed in use much longer. One Trimotor 5-AT, built in 1929, was still being used in Las Vegas for sightseeing in 1991.

Interior of Ford Trimotor with “club” type cabin furnishings