I would like to go to Yixing from Shanghai Hongqiao airport. What is the best and quickest way?

There is no direct transport from Hongqiao Airport to Yixing at 19:00. I suggest you walk about 10 min from Hongqiao Airport to Hongqiao Railway Station. There you can take a train to Wuxi first. Upon your arrival at Wuxi, you have to stay one night at Wuxi. On the next day, you can go to Wuxi Bus Station (next to Wuxi Railway Station) to take a direct bus to Yixing very easily.