The following mastery setup is a good general setup for any jungler in the game. The Tier conditions are not known yet. In this guide i assume that they won't be changed, so summoners have to spend at least 4/8/12/16/20 points unlock Tier 2/3/4/5/6 respectively.
As you can see i prefer offensive jungling. My opinion is that offensive junglers works better. They can clear the jungle faster and can help ganks more. Overall they are more efficient. We have spent 21 points, so 9 left for the Defensive tree.
This is a pretty decent setup for a jungler. The only drawback is the lack of improved Flash spell. Of course others setups can be good too, but maxing out offense is the best i believe. More damage means faster jungling and better ganking.