Should you rent a car in Maremma?

Yes, I recommend renting a car in Maremma if you want to combine beaches, villages and countryside without organizing each day around bus schedules. Trains notably serve Grosseto, Follonica and Orbetellobut they don't take you directly to many beaches or to the inland villages. From Grosseto, allow about 20 km to Marina di Alberese and a little more than 20 km to Castiglione della Pescaia.

Without a car, it's still doable if you choose a well-connected base and accept limiting your visits. You can take the train to Orbetello-Monte Argentariothen continue by bus to certain areas of the Argentario. For Marina di Albereseshuttles run at certain periods, but their days and times change with the season: check them before counting on them, especially outside summer. Connections can also make an outing longer.

My advice: take a car to explore several spots, especially in the countryside or off-season, when buses are less convenient. You can do without one for a stay centered on a single town and a few beaches accessible by bus. In summer, expect beach parking lots to be in high demand; having a car makes travel easier, not necessarily parking.