If I can only visit one city in Italy - which one should I visit?

Tweet

I want to visit Italy but time and money is very tight, so I may not get every where I want to go. My grandmother says to go to Venice because it's sinking and much of it could be lost over the years to come. But Florence is my first choice. But then there's Rome! What would you do? Where should I go??? And is it true that the police officers in Milan where uniforms designed by Armani? wow...