Without knowing our interests any comments on where we should stay for 3 days? Thanks
I just replied to your same question on Trip Advisor.
Innere Stadt. A no-brainer as this is the historic central district where many sites are located.
Every city borough has its pros and cons. Most important is good access to public transport, i.e within 3 minutes walking distance. To make most of your short time you should get acquainted with public transport in Vienna, and use it as much as possible.