Number 5. Nice thirds (snow, trees, sky), nice diagonals (skis),and you can actually see the rider's face.
The last photo is great. I like how the rider fits in the frame and you captured the action at the perfect moment.
I think these were some great action shots. I love the contrast in the first photo between the white snow and the trees.
the first is my favorite, featuring the natural setting in the upper 2/3
five and three are great! they make me feel like I'm there watching it happen.
5 is really great. Great angle, light, color. It has the feel of a captured moment.