Best Beaches in Tuscany?

Viareggio has a wonderful beach as well as lots of activities. Just south of town is a park with piney woods and miles of free beach (Lecciona). There are numerous other choice, it depends on your interests.

I know the Tuscan coast better than the beaches around the Bay Area, where I spend most summer weekends, but in order to give you advice I need to know if you have a car or not. Some are not so easy to reach by train, but if you have a car then the choices abound. Also I'd like to know where you will be in Tuscany for the most part. For example if you are around Lucca area, you probably don't care to go all the way down to the Grosseto area.

Roberto - I would also be interested in your thoughts. We will be driving from La Spezia to San Gimignano via Pisa, so if you have any recommendations for a beach between La Spezia and Livorno it would be greatly appreciated. Are most of the beaches pebbly or sandy? I am definitely after free beaches (I'm from Australia - can not get on board paying to go to the beach) Thanks for any advice

Roberto - you had mentioned Via Reggio in a post last year. We went and it was a highlight of our trip. We did pay for the beach, but it was well worth it. We stayed at the Hotel San Francisco and used the beach club across the street Elisabeth - gret lunch. Really enjoyed our time there and it was very convenient to Pisa ,Luca and Florence by train

Lecciona is free, sandy and as undeveloped as you'll find on the coast north of the Maremma. You can access by pay parking south of Viareggio, or at Torre del Lago.
http://ciaolunigiana.com/beaches-viareggio-versilia-lecciona/

The beaches from Bocca di Magra (border with Liguria) all the way to Livorno are sandy.
Viareggio to Marina di Carrara is a long row of resort towns. Most of them have "beach concessions" called "stabilimenti balnerari" or simply "bagni". Access to the beach is free by law and within 5 meters from the water it must be kept open to the public, however they charge you if you use the facilities (lounges, umbrellas, etc.) provided by the concession.
All of those towns have similar establishments, and at night they offer plenty of "people watching" opportunities.
Viareggio is probably the largest, but Forte Dei Marmi is the nicest with the fanciest people and you might have a chance to meet some famous people there, especially if you go to "La Capannina", a famous club.
Andrea Bocelli lives at Forte dei Marmi and Matteo Renzi (Prime Minister) vacations there, along with many famous people in show business. As a 20 something I used to rent beach houses in Marina di Pietrasanta or Marina di Massa (Forte was too expensive) or even camp at Torre del Lago and use the Lecciona beach. At night however we would always go to either Viareggio or Forte dei Marmi. The latter in the hope to pick up a rich girl vacationing there (never worked out for me, my motorcycle or car didn't meet the engine displacements requirements of those girls) .
South of Viareggio, between Viareggio and Torre del Lago, there is the famous La Lecciona beach, which is part of the park (there is a large pine grove behind it) and therefore undeveloped.
It's also undeveloped all the way to Marina di Pisa.
South of Livorno, two quaint resort towns are Quercianella and Castiglioncello. The train stations are next to the beaches. These are prettier, but the beaches are rocky and with cliffs (similar to Portofino area). It's a bit more upscale than Viareggio, so a bit more expensive.
South of that (Rosignano, Marina di Cecina, Bibbona, San Vincenzo) all the way to Baratti, is sandy beaches with establishments similar to Viareggio, but with plenty of undeveloped beaches between the towns. Baratti is nice, but rocky. Water is clean there. I used to go as a kid when I stayed at Cecina Marina.
The best beaches are probably south of Piombino, in the Maremma area.
The areas of Follonica, Punta Ala, Castiglion della Pescaia, all the way to the Maremma park and Talamone are more unspoiled. Then there is the Argentario peninsula and the Tuscan Archipelago (e.g. Elba, Giglio). Both the Argentario and the islands are definitely the top of the Tuscan coast in terms of natural beauty. There are both beaches and cliffs there, and the water is definitely cleaner. However a car is almost a must for the southern part of Tuscany.
In terms of easiest train access, if you don't have a car, I would definitely choose Viareggio or Quercianella or Castiglioncello (the last two are not sandy, but cliffy and rocky).
For night life, Viareggio, Forte dei Marmi, Lido di Camaiore are the top. For a chance to meet a rich soul mate: Forte dei Marmi, Argentario, Tuscan islands.