Visited Viareggio during first week of Carnival, and stayed at La Petite Maison with my girlfriend. The Hotel is conveniently located nearby the train station and is also walking distance to the city center and the main promenade!
Considering the price I have to say that you cant ask for more: clean room, internet, nicely furnished (every room has a different style!), and an awesome breakfast with all sorts of pastries and cakes. Staff was really nice to us and helped us out finding nice reastaurants for dinner. Overall A+++