I just received my second Kifaru, a ZXR which is SWEET! It's my new favorite pack and I bought it after MUCH deliberation. My other is just a Tailgunner I which is a very nice lumbar pack. I would say Mystery Ranch (from founder and former owner of Dana Design packs) is right there but with more of an emphasis on backpacking than military/hunting. I have 3 Mystery Ranch packs and they carry extremely well. I will say Kifaru IS the most bombproof all around but I don't know that they carry any better. Here in the wet Pacific Northwest it rains a LOT and the 1000 denier fabric used on all the Kifaru packs will carry more water than other pack cloth out there. It will carry the extra weight well though

Kifaru packs are heavy but you will not have to worry about it failing you that is for sure. Put it this way... Mystery Ranch gives me the confidence of an ASH1 LE and the Kifaru gives me the confidence of the ASH1 CG.
[Edited to add... another similar comparison is FBMLE vs FFBM. The FFBM being acknowledged as the toughest out there. We are talking about best of class in both cases IMO)
Kifaru is AMAZINGLY modular but will always look like a military pack.
Mystery Ranch is has it's heritage in backpacking as mentioned.
While I have ZERO doubt in Kifaru's products (I just blew a ton of dough on my new pack and feel great about my purchase), the MountainSmith legacy is not as strong it's offspring.
Comparing the ancestors of these two amazing pack companies can only be stated this way which I am sure you guys will appreciate...
Back in the day I could cut your MountainSmith pack in half with my Dana Design pack

. Dana Designs packs back then would carry loads that would turn other internal frame packs into bean bags. While Dana Gleason of Mystery Ranch is still a genius in anatomical load bearing systems, Others appear to be right there and Kifaru packs will carry a staggering load very well also. Dana Designs was sold away years back and they are mainstream packs now with cheaper materials and overseas manufacture. Mystery Ranch is made in Bozeman, MT and Kifaru is made in Colorado. Attention to detail from both companies is remarkable. I am still finding features on my new Kifaru... it's AMAZING.
These days I would trust either of these packs under VERY tough conditions and I give the nod to Kifaru for toughness and making packs that are better suited for taking your Busse knife for a one, two or three walk in the woods (patrol packs). This is to say that I just like their small bags better than anything else out there, not that their large bags will leave you wanting in any way.
Just my two cents
Packs currently owned...
Dana Design Alpine 5000 ci
Mystery Ranch Kodiak 7000 ci
Mystery Ranch Big Sky +/- 3000 ci
Mystery Ranch Longhorn 2300 ci
Kifaru ZXR 3800 ci
Kifaru Tailgunner I 900 ci
My next pack will be another Kifaru most likely.