chest mount looks more like a true POV because you can see the arms and sometimes knees / skis, which i think is really cool for POV. it makes watching the video more exciting and feels like youre really there.
the helmet cam, on the other hand, makes you feel like your 6 feet above the skier and the footage tends to be more boring. it feels slower, doesnt show very much detail of what youre actually skiing on (because its farther away from the snow) and its really easy to point it too high or two low. also the camera is more exposed and will break off easier from the helmet.
the pole mount gives cool angles when its pointed at yourself, and it shows all the sweet face shots and such, but i really hate not being able to pole plant, especially if im skiing something worth filming.