I hear great things about mystery ranch, can't give any input on them as I've never tried one. Same with Kifaru and KUIU.
What I do know is that I really like my Eberlestock J34
. The layout and expansion fits my use very well. I've had over 70lbs in mine and been fairly comfortable. For me much more than that isn't comfortable with any pack, I just do it anyway. The eberlestock
's advantage to me is that is works really well as a daypack and can function to do everything else. I use it mostly as a daypack. If I really wanted it primarily to pack a load and still function as a daypack I might look at something else. The biggest downside I see to an eberlestock is that they expand out instead of up so if you have meat in the main compartment and then add camp to a duffle your center of gravity is further back. The biggest upside for me is that I can use it as a nice comfortable daypack, then still get a hindquarter and the backstraps of an elk out with me efficiently after I shoot it. That makes one less trip later. I find the scabbard pretty quick and convenient also. The first year I had mine I jumped a coyote from a patch of brush and killed him 47yds from the patch if I remember right. It's been a couple years and I wouldn't swear to that distance without checking my old post. I know when I spotted him I had the gun drawn and on him without thinking, that is what counts for me.