eh, thanks all!
@sinned79, I read from forums, BaDaLing is always flooded with visitors (my tour guide said 20x MuTianYu's crowds). So I eventually chose MuTianYu which is further away from BeiJing. Nevertheless, there were much lesser crowds! I don't think you can get similar view (with <20 people in this photo) at BaDaLing. I've never been to BDL, but I heard MTY is steeper than BDL, and it offers better scenery as well.
Just to share with you, IF (and only if) I have chance to BeiJing again, I'm going to concur this part of Great Wall: