plan to visit Suzhou when in Shanghai, what is the most interesting place to go in a 1 day trip

At Shanghai Railway Station or the local Hongqiao Railway Station, you can take a high-speed train to SZ in about 25min. Upon your arrival, the Sister Gardens cannot be missed. To have a good visits at the gardens, it may take you a whole day. Or you can spend one day at Tongli Town to experience the local people's life.