Florence is the epicenter of tourism, be it for its artistic value, architecture or simply for la vita Fiorentina (Florentine lifestyle). There are approximately 10 million visitors traveling to Florence at a yearly basis from all over the world.
The best period to visit is from late March to Early June or even from mid September to mid November. Avoid the July-August months since it gets extremely hot and the streets are packed with people. It could be a better option traveling to the sea side like Isola d’Elba, Sardegna or places in south Italy. December-February get pretty cold and temperatures do drop considerably. Personally, in the winters I would I choose the ski destinations like Sud Tirol and le Dolomiti located in the North of Italy. In general the best time to enjoy Tuscany as a whole is in Spring.