If you must, spend the most 2-3 days in Budapest, but Vienna is lot more fun and interesting. In February the weather is brutally cold. If you have HH points, book the Hilton in the Castle district, very nice place. Be careful with taxis, they are notorious for ripping-off tourist. Also the restaurants have a nasty habit of overcharging tourists. I guess the communist habits are hard to break. I will spend more time in Vienna. Taking the Ralijet from Keleti is easy and very comfortable; in less than 3 hours u are in Vienna. If you book the ticket online http://www.oebb.at/en/ with few days ahead you, can get a ticket for as little as 19 euros.