Which Chongging or Chengdu closer to Xian

I want to tour Xian from 17 to 26 June 2014. I want to fly Air Asia however it does not fly there until July.
It flies to Chengdu and Chongging, so which city should I fly to and from there is the rail or coach journey too long.
I dont like sleeper beds , much better to have reclining soft seats.
Should I take a coach or train. Which stations in the two cities and Xian for either one?
Thank you.