That all depends on what kind of performance your wanting and how big your plane is, if you provide the following info it will make choosing a prop and proper gearing MUCH easier.

1. What kind of plane is it?
2. How much does it weigh?
3. What kind of performance are you wanting?
4. What is the normal operating voltage for your motor, 6v? 7.2? 8?
5. How much are you willing to spend on upgrades?

If your wanting good 3d performance everyone is going to want you to go brushless, and for a good reason!