I think either size would work for you, but I prefer the 17. I have the 17 and it fits similar to your pics. I like the fact that I can push it down my arm a bit and I never feel it's too loose when worn closer to my wrist. I can also turn mine easily, but it can't turn on its own. I haven't had mine long enough to experience the summer months yet, so I can't comment on that. Good luck with your decision! 
