So far, it looks like it's an Apple's iPad market in China. In the last three months ending July with Apple only beginning to sell the iPad 3 in late July, the iPad has a 72% market share compared to everyone else with mainly Android tablets bringing up the rear.
It'll be interesting to see where Surface sits when it begins selling in China. Windows is very popular there so it's possible that Microsoft could have a shot at second place down the line.
Regardless of what happens, the iPad isn't likely to have such a dominating share as other tablets with newer devices like cheap 7" versions hit the market. However, the Chinese market is huge so there is plenty of pie for everyone.
The question is where devices like the Nexus 7 will fit into all this and if Google, Microsoft, and Lenovo can afford not to take some risks to gain sales quickly. Let's see how Surface or a variant from an OEM does there against the Android tablets.