Adding some thoughts here following our trip in case anyone does a search for the same cities …
Tantris was underwhelming. The room is striking, the food was good (not great) but overpriced, and the service was poor. Seemed as though they might have been understaffed. The somm, Justin Leone, was an exception. He was engaged and helpful. I would not make a return trip.
Spatenhaus was good, Pfistermuhle was OK, and the Augustinerbrau Keller, a massive outdoor bier garten, was great for lunch although dinner on Friday night was a madhouse to be avoided. Schuhbeck’s is good old-school fine dining, if you like that sort of thing (i.e., a little stuffy).
Onyx was easily the best dinner of our trip. Splurge for this one if you have a chance. The International Tasting Menu was fantastic, including the breads and desserts. Room and service were also first-rate. Wines not so much—mainly Hungarian, adequate but no better than that.
Borkonhya Winekitchen was the first restaurant that I’ve exited without eating my meal since Pizzeria Uno in Forest Hills, ca. 1985. A one-hour wait between courses was the trigger. (The bread and appetizers weren’t that good either.)
Mak Bistro was an interesting hipster-ish dinner place. Good vibe, enthusiastic wine service, inventive “modern Hungarian” dishes. Not too pricey and definitely worth a try.
Plachutta has basic traditional Austrian food. There’s nothing thrilling here, but if you want a place to try Wiener schnitzel, you could probably do a lot worse than this place.
Rote Bar in the Hotel Sacher … meh. The others in my party wanted to try this old, traditional place which is the home of Sacher Torte. It’s very red.