Vienna 2-3 days

The best spot to sleep is in the Ringstrasse, a.k.a. the ring and old center.
You don’t have time to take day trips because there’s lots to see. One night consider seeing an opera. You can check their website to see what’s playing, if you decide to go, you can purchase standing room tickets 1h 20m before the performance for 3EUR.
Vienna’s must see sights are Hofburg Imperial Apartments, Treasury, St. Stephan’s Cathedral, Kunsthistorisches Museum and if you have time, Schonbrunn Palace.

Food we enjoyed in Vienna is apple strudel and Wiener schnitzel. If you like chocolate( we don’t) sacher torte is famous there too.
Stay on the Ringstrasse as noted by above poster. Honestly, glad we visited but have no desire to return there.

https://www.pension-suzanne.at

Near the opera house and the u-bahn station just inside the Ringstrasse.

The Kunst Historische Museum has an amazing Egyptian collection due to Franz Josef's patronage of Middle eastern archeologists sweeping up all the neat stuff from the poor citizens of the Ottoman Empire. It was good to be the Emperor.

We loved the Schonbrunn Palace, and rate it higher than RS does in his Guide Book. The grounds and gardens are impressive. We found that one of the multi-day museum passes met our needs nicely, as it included the Hop On-Hop Off bus, a boat ride, and practice sessions for the Lipizzaner stallions.
The service and the breakfast at the Hotel Am Stephanplatz was wonderful, and it is directly across from St. Stephens Cathedral.

We will be in similar circumstances for our April Italy trip- just waiting for British Airlines to extend their dates for flight changes.
Safe travels.

The standing room opera tickets are now 10Euro but a great experience. Public transportation in Vienna is amazing so I would use that to get around.

With 2-3 days, you do not have time for side trips.

I got the Sisi ticket and did the Schonbrunn palace as well as Imperial apartments. I also really enjoyed the Opera house tour and St Stephen's cathedral. I did the tour of the catacombs which was very neat.

Food wise, if you are a coffee drinker, you are in for a treat. They have amazing coffee. They also have amazing pastries and the Sacher Torte is worth a try for sure.

We stayed at the Rathaus Wien in 2015 and would gladly stay there again. You don't sound like art lovers, so I'll spare you my favorite places. I agree with Pat that the Vienna Pass is an excellent value for money.

Fromme Helene and its neighbor, Marienhof, were our favorite restaurants.

https://www.hotel-rathaus-wien.at/en

https://www.frommehelene.at/index.php?id=3&L=1

http://www.restaurant-marienhof.at/restaurant/?utm_source=restaurantguru&utm_medium=referral

The Opera House tour is very interesting, but not included in the Vienna Passes, but I think it was only about 10euros.

We stayed at the charming Hotel Austria. It was walking distance to most sights and restaurants, but was away from the main tourist scene. Our favorite sites: Schoenbrunn Palace (we reserved online), Opera House Tour, Kunst Museum, Lippizaners Horses, The Third Man Museum for post WWII history. The Belvedere and Albertina Museums, Naschmarkt for lunch, Lugeck for a traditional Viennese Menu, and Da Capo for Italian cuisine. I would suggest restaurant reservations. Just walking around Vienna takes your breath away. The architecture is stunning. BTW, we were also in Budapest and Prague last fall. Good "last minute choices!"

We always stay in Vienna at K&T Boardinghouse--one metro stop (3 minutes) outside the Ring. The metro station is 50' away (across the street), and there is a thriving street scene in the neighborhood. The rooms are huge and impeccably clean. We started staying there 20 years ago when we read that's where Rick Steves stayed when he was in town. Great location and the price is right.
KTBoardinghouse.at

There is a walk you can do to see a large number of Jugendstil ( Art Nouveau) buildings. It starts near the Karlsplatz Ubahn station, goes along Friedrichstrasse, and continues along Wienzeile. If you cross over at Pilgramsbrucke and return on the other side of Wienzeile, you can get good views of the buildings on the opposite side. You can do it yourself (we did); but if I remember correctly, there is also a guided tour available through the TI office.
In the same vein, the Municipal House in Prague is not to be missed. Entrance is for guided tours only. The tickets are very inexpensive. As I recall, you can just walk up to the booth, find out times for English tours, and buy tickets.

"You don't sound like art lovers, so I'll spare you my favorite places."
Estimated Prophet,

We're going in 4 weeks and love art. What do you recommend?

Debbie - I sent you a PM

We just got back from a Prague, Budapest & Vienna trip. We stayed at a small hotel in Vienna that was just catty corner from the Opera House on Opernring and we loved it! The trams stop right near the front of the hotel and the Karlsplatz Metro station is about a 5 minute walk from there, There’s a lot to see and do, and plenty of restaurants and shops, all within a 10 minute walk. The hotel gave us a free upgrade to a room with a balcony that overlooks the Opera house and a very nice breakfast was included.

I'll continue to pimp for my favorite place to stay in Vienna - Pension Kraml http://www.pensionkraml.at/ Family owned and operated. Very reasonable rates in a great neighborhood. Staying in/near the Ring is nice but it sometimes can limit the scope of what you visit in the city.

If you are into the offbeat, then use Atlas Obscura: atlasobscura.com/things-to-do/vienna-austria/places

Honestly, there are so many "must see" places in Vienna you could easily fill 5 - 7 days and then just skim the surface. I've spent a whole day just photographing churches in the city. It all depends on what you want to do with your time.