I bought both sizes and I am on the fence with the M/L (18-21). I am 18"/175lb/5'11 and having just tried on the S/M (16-19), it feels pretty snug. A tad high on the hip and not much play with the shoulder straps etc.
New to Osprey. My summer pack is a camel 22L and winter is a 35 Gregory. So the I am in different territory.
Looking to add abit more weight for alpine endeavors which brought me to the AG.
Anyone have any experience with this model? thanks! J