It depends on how much space there is. I needed the longer one because something would have been in the way with the shorter one next door. If there is enough space, the shorter one, and if not, the longer one.
Hello, I have the same holder on my bike and am very satisfied with it. I'm not permanently on single trails, but I can say that when riding off-road, the holder holds the mobile phone perfectly and also cushions it slightly against impacts. I am very satisfied with it and can only recommend the product.