Train or flight from Shanghai to Guilin?

I will be traveling with 5 adults and 1 8-year old in December from Shanghai to Guilin (then drive into Yangshuo same day).

Would you recommend taking train (7-9 hours) or flight (2-3 hours)? Cost is about the same.

I've read that some recommend a cut off of 6 hours to opt for train, but is it a bad idea to still take the train route for a more hassle free trip?