I would always choose my case study over other options and I feel that case study questions tend to be broader as they have to apply to so many countries. Because they are broader you can write about a lot of stuff and still be right, in my trial I had a question like "Discuss the policies used to promote economic growth and development in a country other than Australia" which is a very easy question to answer. I would def recommend knowing your case study. You also need to remember that if you don't know anything about ur case study and it comes up you will have no choice no matter how bad the other option is.
If you have the Riley textbook there's a China case study that is already done for you and you just need to memorise it.