We were there last March/April 2018.
Three nights were spent in Prague: Walking Tour, Easter Markets, Charles Bridge, Prague Castle/Cathedral, Jewish Quarter, Mucha Museum. We stayed at the Hotel Metamorphis in the Old Town: lots of steps, no elevator, but an incredible breakfast!
We used CK SHUTTLE, the service recommended by RS, to get from Prague to Cesky Krumlov. The drivers were delightful, professional, and had a great command of the English language. The vans held nine passengers, and pick up/drop off was at our hotels, and the trip was about three hours.
We loved Cesky Krumlov, spent two night in the Castle View Apartments, in the attic studio apartment- with a castle view. [This apartment was shown -quickly- in one of RS' videos.] We did the free [for tips] walking tour, and just wandered. Lots of beer lovers here!
We then used CK shuttle to travel from Cesky Krumlov to Hallstatt, [three plus hours], spent one night in Hallstatt, and did the very interesting salt mine tour, 4000' above the lake. Not all businesses were open in Hallstatt, as it was early in the season, but it was definitely worth visiting.
We wanted to go to Melk/Krems area, but once again, were a little early in the season, and the river boats weren't running daily yet.
From Hallstatt we took the delightful ferry to the train station- to Salzburg, and spent three nights in Salzberg, in the Old Town area.
We did RS' walking tour, went up to the Fortress, walked to the nearby beer garden, and attended a music concert. It happened to be Easter Sunday, and altho not religious, we attended the most glorious Easter Mass service in the Cathedral: some of the music was originally written to be performed in that same cathedral. The orchestra and choir were magnificent ! We stayed in Old Town, at the Boutique Hotel Am Dom. Breakfast ok, but room was very comfy.
From Salzberg we took the two hour train to Vienna, and spent three nights in Vienna. We purchased the three day Vienna Pass, and for us it was cost-effective: Schonbrunn Palace, on/off bus, Natural History Museum, Kunsthistorisches Museum, Hofburg Palace, Spanish Riding School, and the Belvedere. The Opera Hour tour was not included in the Vienna Pass, but it is a great tour. We stayed, again in the Old Town, right across from St. Stephens Cathedral, at the Hotel Am Stephansplatz: great breakfast and incredible service.
Feedback: I want to return to all the cities visited, [except maybe Hallstatt- one night was sufficient.] The Easter Markets were a pleasant surprise, and added a festival atmosphere. The weather was cool, but we had our layers, [and a scarf and ski cap], and were comfortable. [We travel carry-on luggage only.]
We did miss the blooming flowers and the leaves on the trees- we were too early for the spring foliage, and if I had a choice again, I'd go later in April. And- being there at Easter was wonderful.
Safe Travels, and sorry this is so long, but I enjoyed reliving our trip!