Which European City do you think would be most enjoyable for a young person to Live in out of this List?

I would definitely have to say Vienna. I lived there for 3 months and wish I could go back every single day. It is so beautiful and so safe! I would have no problem walking around the city at night alone. It also has so much to do all the time. I would not suggest Florence or Prague. They are more touristy places and don't have all that much to do. Barcelona is pretty up and happening, though.