Tough question and it took me over a year to decide and pull the trigger. Damn expensive, but the search for perfect boots is worse.
I tried on Kifaru, EXO, Kuiu, Badlands, Stone Glacier and eberlstock. Kifaru, Kuiu and EXO I visited their home office and they sized me right there until they got the fit right. I tried to wear them with 60lbs in each, but it wasn't always easy and hard to do apples to apples comparison, especially given the time lapse between each. They're all pretty high quality, but frames in the Kifaru, EXO, Kuiu and Stone Glacier really felt solid. Best thing to do is hit up one of the bigger shows where they all attend.
For each of those brands there was something in the design I didn't care for...not really negative, just splitting hairs on little features. But there are things to look for and decide on. i.e. do you have a straight back or sway back. How long in your torso and how well does each pack accommodate. Do you want tons for features, straps and pockets or go minimalist. Do you want a load shelf? Do you want it to be bomb proof? Are you buying it for the 90% of the time you're using it or the edge case (i.e. 3 day hunts vs once in a lifetime 14 day hunt) or (heavy loads long distances vs occasional heavy loads short distances). Do you want it light weight? Modular bags and/or pockets? There's pros/cons to each decision. Really "fit" is most important, but also super hard to test because you won't really know until you carry a moderate to heavy load a long distance with vertical....which lets be honest, that rarely happens.
I never got to try Seek Outside, but I really wanted to because I am a fan of their frame and the modular design of adjusting the height of the load lifters. The physics of it make sense to me. I tend to pay close attention to design details for functionality and materials. I couldn't find any Mystery Ranch packs, but felt they were very similar in many of those tradeoffs as Kifaru. Kifaru was really stiff, felt like a board and didn't fit my back, heavy pack, tons of options for bags and accessories, nice hip belt, but maybe over-featured for me. The EXO packs were sweet and my second choice, but that upside down U shaped titanium frame just seemed like something could happen to it. Yet I've never heard of issues. Hip belt was comfortable, but maybe too basic. Kuiu was super light weight, nice packs, great value, frame seemed stiff, but their carbon frame has plenty of doubters too. The hip belt didn't sit well for some reason. In the end I went Stone Glacier. So far I'm super happy with it. Minimalist, light weight, great load shelf, very nice hip belt, etc. Just wish it came in camp. Is it really better than others, who knows, but given all the tradeoff decisions it matched up best with my criteria. I will say this and I assume this comment represents most of these packs, having a quality pack really made a big difference. I was using a high end mountaineering pack in the past and the SG pack was a big improvement....way more than I expected. Not just in carrying heavy loads, I expected that, but also just how comfortable it felt hiking in general with camp on my back, covering distance. Now I feel like my old pack was a piece of *)&(^& and I should have upgraded sooner.
Good luck!
