It's quite an amazing scene that I see people holding ice cream at 10am, lunch time, dinner time and late at night. It's not just one scoop, but double or triple. I believe Vienna may be the city that I have seen so many people getting ice cream as well as many ice cream shops. Most of all, all the shops are in long lines. So the one without a line should have a problem.
Photo 1-4: this is the first try and the least better one - Castebello - the shop has very good seating area. 5-6: Stanizel - this is a very classic shop and the cheapest one but the best one among all the 3 we tried. Last photo: this one has a constant long line whenever I passed by it. As I saw only 7-8 people, I then got in the line and got one. It's quite a nice one though I prefer Stanizel.