Choosing a pack is like choosing boots. Most important is the fit and ergonomics need to match the user's build while still being able to support the intended extra gear. Try on different packs and if possible, drop some extra weight into the pack. I always liked the idea of the weighted bundles that some stores keep near their packs so shoppers can get a feel for how a pack carries. Figure out what you need to carry, then buy the pack that suits your fit and preferences. Just make sure it is big enough. More space is better than less space. Most outdoorsy types will eventually have multiple packs in the gear locker to accommodate different activities and varying quantities of gear. I probably have more than 30 different packs in the storage room.
I lean towards lighter weight packs that can comfortably carry heavy loads. My primary, general purpose, hunting packs are from Arcteryx. I have the LEAF Assault 30L and 45L. For most of my hunting, the 30 is all I need for day hunts away from the truck. I grab the 45 if I need to carry a bit of extra food, water, or cold weather gear. For multi-day hunts with a lightweight tent and/or biv bag, and depending upon the terrain, I use a Lowe Alpine Sting 55L, a Lowe Alpine Contour 3 60L, or an Arcteryx Nozone 55L. For longer trips in the mountains that require extra gear and the potential for needing to cape, debone, and pack an animal out, I use a Lowe Alpine Saracen 120L.
I do not own any Mystery Ranch packs, but I do like what I have seen as they seem well built and are relatively light but I have never had the opportunity to load one up and experience how it carries. I was quite drawn towards the specs on a military style 50 litre pack they made for the Yanks but I do not need any more gear. Badlands makes some good entry level gear for lighter loads; I have a couple of their small packs, but their harness systems need some work. I am not a fan of anything from Eberlestock as they seem ridiculously heavy without having any gear loaded. Quite a few of my buddies have Eberlestock gear and they all seem to like it, but they are too heavy for me. I also do not like the dimensions. I am 6' and have a 46" chest. I find the Eberlestock harness system rather snug and the geometry puts the hip pad well above my hips. Most of my buddies with Eberlestock packs are much shorter than me. Not to dissuade the OP from Eberlestock, but try them on before you buy.
