Advice Best Excursions for Treasures of the Aegean Tour?

We're booked for the Treasures of the Aegean tour this May and are trying to decide on which island excursions to choose. There are so many options, and we want to make sure we pick the best ones for our trip. Has anyone done this tour before and can recommend which excursions are must-dos? We're particularly interested in historical sites and scenic views but open to any suggestions that made your trip memorable.