When I first got this pack, I have to admit, it wasn't my favorite. The neckline in the back is really high and I felt like it might rub uncomfortably. Boy was I wrong. This has quickly become my favorite running pack I've ever had, over Salomon, Raidlight and Camelbak. I LOVE how form-fitting this is. It doesn't come low on my back, so I can even wear it with crop shirts. I love how much I can fit in it, despite it's seemingly small size. I can carry 2+ flasks, my phone, a jacket, and plenty of food for hours and hours out on the trail. I highly recommend this pack!!
For reference, I am 5'5", 108lbs, AA chest and I have the small.