I exclusively use trains here in China, its way chiller than flying and total time doesn't really differ.
We wanted to buy train tickets the other day, but it was just a lottery and no way to actually buy tickets in advance, do you know what's up with that? Buying flights was just normal so sadly we just did that.
Tickets are released only 15 days in advance. Popular lines tend to get sold out quite fast. Especially around festivals.
The sleeper cars are pretty nice for long hauls, too, why spend a day traveling when you could spend a night.