I ride 15/-15. With most new riders that dont know what angles will be comfortable I tell them to jump and do a 180 and land with their feet just wider than shoulder width. Do that several times and get a good idea what angles your feet are at. This is going to give you a good idea of what angles your knees and ankles will feel most comfortable with when riding. Most people land around 12-15. The width of your stance is obviously going to play into this too, but in my experience a wide stance is better for balance whether your freeriding or in the park. I ride at 23.5".