I am considering a one or two day rental for day trips. Where shall I rent a car in late May? Public transportation would work, but I could see more sights and have more time and freedom with a car.
At the main train station in Salzburg you will find Sixt, Thrifty, Hertz, Europcar, Avis and Budget. These are all major international car rental companies with websites where you can search prices/options. I typically use an aggregator like Kayak to quickly find the best prices, but rent directly from the rental company instead of a third party.