I recommend Tongli, but Zhujiajiao is much closer to Shanghai. You can do the tour your own. Well, it is better if you want someone to explain the old town to you. If you want to travel alone, you can prepare and search something in internet before going. Take bullet train from Shanghai to Suzhou, first, only half a hour. Get out of the railway station of Suzhou, cross the bridge to Pingsi Road. There are shuttle bus to Tongli every half a hour. You can take a taxi from Suzhou Railway Station to Tongli, about 100RMB.