Getting to Zhangjiajie or Changsha from Hong Kong

We want to take a 5-7 day tour of Zhangjiajie and Tianmenshan and Fenghuang town (all 3 places is important). We want to fly to Changsha or Zhangjiajie from HK to begin the tour. There are no direct flights to these cities from HK, so we have to go Guangzhou or Shenzhen to start. Which one is better to fly from? Also, I need the name of good, reliable tour companies offering this tour from either Changsha or Zhangjiajie, please.