I'd recommend train, since you can see much on the way and trains are a real experience in China. Just book well ahead ... I think they are expecting 230 million people travelling home this year for the Chinese New Year, and last year there were something like 800,000 camped out at Guangzhou train station all trying to get tickets.
Guilin is on the way - hire a bike and cycle to Yangshou, beautiful landscapes. almost 10 years ago