Vienna and Salzburg both trade on Austria's imperial and musical heritage, but at very different scales — one is a former empire's capital, the other a small baroque city best known as Mozart's birthplace.
Vienna's Schönbrunn Palace, Hofburg Imperial Palace, and Belvedere Palace reflect centuries as the seat of the Habsburg Empire, each a half-day visit on its own. Salzburg's Hohensalzburg Fortress and Mirabell Palace and Gardens are smaller in scale but arguably more scenic, set against the Alps rather than a flat cityscape.
Vienna's classical music pedigree runs deeper and broader — the Kunsthistorisches Museum is one of the great art collections in Europe, alongside a live concert and opera scene without rival. Salzburg's draw is more personal and specific: Mozart's Birthplace (Geburtshaus) and the city's setting as the filming location for The Sound of Music.
Vienna is a major European capital, spacious and grand, with the Innere Stadt (1st District) alone worth a full day. Salzburg is compact enough to walk end to end in an hour, its baroque old town wrapped tightly around the Salzburg Cathedral (Dom) and hemmed in by mountains.
Vienna is well set up as a base for a longer Austrian or Central European trip, with excellent train connections onward to Budapest or Prague. Salzburg's compact size makes it better as a one- or two-day stop, often combined with the nearby Austrian Lake District or as a stopover between Vienna and Munich.
Choose Vienna for grand imperial palaces, world-class art, and a full capital-city classical music scene. Choose Salzburg for a smaller, mountain-backed baroque city with Mozart's legacy and Sound of Music charm. They're under three hours apart by train, making a combined Austria trip straightforward.