Taiji Cave, Shanjuan Cave and Xishi Cave are the most interesting.

Considering the itinerary, transportation and accommodation, I think Taiji Cave is the most interesting.

1. Itinerary: Taiji Cave and Xishi Cave are underground caves, but Taiji Cave is more magnificent, with more scenic spots and landscapes and longer tour time. Shanjuandong is dominated by waterfalls and underground rivers, and the time is relatively short. Therefore, from the perspective of the itinerary, Taiji Cave is more abundant and substantial.

2. Mode of transportation: It is the most convenient to get to Taiji Cave from Shanghai, and the expressway and high-speed rail are direct, which takes about 3 hours by car. Shanjuan Cave is located in Yixing City and has convenient public transportation. Xishidong is located near Shaoxing city, and the traffic is relatively inconvenient, so it is necessary to plan the route in advance.

3. Accommodation: There are many hotels and homestays around Taiji Cave to choose from, and the prices are reasonable. Shanjuan Cave is located in Yixing City, with many accommodation options. Accommodation around Xishi Cave is relatively less and the price is higher.

To sum up, Taiji Cave is the most interesting tourist attraction in terms of itinerary, mode of transportation and accommodation. Of course, the specific choice still depends on personal interests and preferences.