BTC38 has the most volume by far, but it doesn't have any btc pair (i.e. you have to exchange to/from CNY as an additional step), furthermore it is laggy and has a bad interface. But it's where the game is played, so it might be at least worth trying.

Novaexchange doesn't have the above issues, but very low volume.

I suggest you try both with little amounts, so you get an idea of how they work, without any risk.