Everything locallady mentioned can be easily done in 2 days, 3 days if you are very slow.

Vienna is a world class European capital with exquisite restaurants, famous music halls, grand architecture, unparalleled majesty, museums, parks, sopping, not to mention the best pastry I ever have; and these are just a few of my favorite things. Budapest, on the other hand, a cement-gray town full of old communist relics, graffiti, perfectly priced for people who want to experience the grandeur of the Austro-Hungarian empire but can afford only the Hungarian part.