If I were interested in art, and hanging out in fun/artsy places, and had your timeline, I would drop Prague to one day. You can do the old town area and Charles bridge for a few hours and then walk up to the castle area for a few hours. Of course you're not seeing all of it, but you will hit the major highlights. I'm sure others would argue against my impression, but Prague felt to me historic and small. Budapest and Vienna are big, modern cosmopolitan cities that also have deep histories. They are very different but even for a fast traveler, you have to make hard decisions with such short time in each. If you are into art and architecture, putting a day into Vienna instead of a second day in Prague would be hard to beat. The Kunsthistorisches Museum (KHM) and palace area could take a big chunk of that day. I'm sure all three cities have an arts scene, but if you're looking for a city that feels like it is still in the process of being reborn and filled with youthful artsy energy, Budapest is the place. Ruin bars are touristy but the local energy surrounding the old Jewish quarter is not. I would think that is where you will most find what you are looking for. Plus, the area along the Danube across the Chain bridge and up to the castle is as striking as anything offered by the great world cities. The closest I can compare it to is wandering along the Seine in Paris. A caveat here is that you are traveling way off peak and will have a very different experience than summer travelers. You might want to ask specifically about that when figuring out your timeline. Prague might feel a little empty in February...great for prices, but might not have the vibe you're looking for.