STEPHANSPLATZ - Although Vienna is not known in the same way for underground art as Berlin, it offers substantial squares and promenades for buskers looking to earn their way through this amazing city.
Although the city requires a permit (~30€), there was zero enforcement for the week I performed there, nor were any other street performers playing with a permit. Busking proved lucrative where street traffic is plentiful.
The best spot to busk from what I saw was in Stephansplatz and along the nearby promenade. Get there early to beat out the competition.