We tested and score this metric in various ways. Firstly, we just went hiking! We used each pack on both long and short hikes, with light and heavy (for a daypack) loads, and kept notes on how comfortable we felt in each one. We also examined each bag's padding (or lack of), hip belt, attempts at ventilation, and whether there were any annoying features or pressure points that impacted our comfort.
While hiking in each pack we used and explored all of the various features each one had available. Then we rated them both for the number of feature options available and also how useful they were. For example, we liked the quick stow method for our trekking poles on the Osprey models, but it wasn't a comfortable method to hike with over long distances. Sometimes less is more too, as a pack with a ton of extra webbing or attachment points can quickly become a Christmas tree of hiking gear.
We compared the weight of each pack, and also tried to note whether the differences on the scale added up to noticeable differences on our backs. We also explored the different methods used to make packs lighter, like less padding and thinner materials, and whether those weight savings were worth it from a comfort or durability perspective.
In order to test and score for adjustability, we considered a few different things. First, we noted whether the packs were available in one size only or multiple sizes. Packs got extra points for having more than one size option available. Then we compared how adjustable the packs were on our bodies. Was the torso length adjustable, how did the hip belts fit and could they accommodate a range of hip sizes, and if there were any load-lifter straps on the shoulder straps (and if there were, did they actually work?).
Finally, we scored each pack for durability. Of all of the categories that we rated these packs on, this was the least "hands-on," as there was no way we could get a year or two's worth of hikes on each pack during one summer. What we did do was look for any immediate signs of wear or weak points on each model, research online user reviews for each one and look for durability issue patterns, and then compared the deniers of the bags and whether they had a double or thicker bottom or not. While a thicker material is not necessarily a sure sign of longer durability, in our experience a thinner denier is more likely to wear through or catch a snag than a thicker one.