I am sure that both are very fine organizations and at this stage in your development, either would be a good choice. If you plan on being a Mechanical Engineer, I think the Civil Air Patrol might be a slightly better choice as it might be a bit more technical. But think of it this way, which ever one you pick, it might help you to decide between the two different career paths you mentioned. Maybe, after making your choice, you discover that it is really not for you. That would be a vary valuable piece of information and help you to refine your future career choices;.