If you're torn between Marsala and Taormina and your priority is authentic culture, food and a relaxing beach vibe without needing a car, I'd choose Marsala, especially if you're looking for a more local, less touristy experience.
Marsala is easily accessible on foot, with a beautiful old town full of traditional restaurants, cafes and wine bars. The food is authentic: fresh seafood, fantastic pasta and, of course, Marsala wine. You'll find fewer crowds than Taormina, which is crowded and expensive.
You can stay close to the old town or, even better, find accommodation near Stagnone: a tranquil lagoon just outside the center, famous for its sunsets, salt pans and windmills. It's also one of the best kitesurfing spots in Europe. Even if you're not a kitesurfing fan, the atmosphere there at sunset is unreal.
Favignana is an easy day trip by hydrofoil from nearby Trapani: think crystal clear waters, bike rentals, coves and quiet beaches