If your engine is a 40, the 10x6 will be fine.

If your have a 46, I suggest an 11x6 prop.

The Master Airscrew props (the black ones with the squared off tips) are usually best for a trainer as they are less efficient and will allow the plane to fly a little slower (they also are less susceptible to breaking if you hit a tip on the ground). As your skill improves, you may want to consider going to the APC brand of prop (gray with a tapered, rounded tip). The APC props are more efficient and will thus let the plane fly faster.