plane, its the fastest,
  I've been on the ocean and the sea was so rough that the ship was cork screwing (going straight bow down and then going right up on its side), train and bus can be rough rides, altho I like the train.

Assuming it is for travel rather than commuting it would be train every day of the week. Safe and either relaxing in a modern high speed train or mixing it with the locals in a hard sleeper train offers an experience and travel all in one. You get a look at the countryside as you pass. To me that is the drawback of air travel. You see nothing of the places in between.  

Depending if for business or pleasure. 

My top choices would be train or plane, depends on how in a hurry I am and where I am going.
Why?.  Confort, personal liking of both, safety records.

Next choice will be ship or boat or ferry if available.  I have been a sailor on week ends and vacations, so the sea does not bothers me.

and last,

The BUS.  In China, the only way you will get my butt on one is if there is no other way, including walking there, and you must get me drunk first !.

You're question is too vague to get an answer.   Not too many chances to travel anywhere in China via boat.  Train works great when you go visit your family for New Years.

Me, personally, I'm a cheap bastard and use the bus for most trips.  For business then I go plane and send the bill to my company.

Why isn't car a mode? I love road trips.

I think the train with the sleeping bed is the best. The bus with the sleeping bed is ok but there is no toilet available you have to wait for the rest stops