I have used and owned some of the smaller Sitka packs in the Flash 20 and Whitetail bucket and the Sitka packs lack a load shelf feature and the customization of waist and torso sizing to get a custom fit compared to Mystery Ranch, Exo Mountain Gear, Kuiu, Kifaru and Stone Glacier. The sitka packs are nice in that they come loaded with waist belt straps and a rain cover instead of buying those seperately. I wear a lot of Sitka clothing, but don't care for their packs.
Kuiu packs are probably the best value out there right now.
Tenzing isn't great on build quality or weight.
Ultimately you have to pick the pack that fits you and your hunting style. Any pack from Mystery Ranch, Kuiu, Exo, Kifaru or Stone Glacier that fits you is the way to go. I use the Mystery Ranch Metcalf and love it as I could get an XS waistband with a large torso. Go to an REI or similar shop to get your torso and waist belt sized.
I have three friends with newer Kuiu packs. All seem to be pretty happy, two of them packed some big loads out of wilderness areas and I didn't hear any complaints from them. If those were the three brands I was considering I would go Kuiu.
I have a Sitka Bivy 45. Have only used for training trips thus far - loaded with my rain gear, day gear and 10-Liter water bladder for added weight - about 40-lbs total. It holds the weight as well as any other quality backpack - waist belt cranks down nice and snug - this is most important feature as I have returned a few expensive packs that I could not keep riding on my hips. Design wise, I would lose some of the additional zippers to lighten the thing, enlarge the back pockets to fit a full size spotting scope, put a more sturdy side pocket (it is mesh) so that can be used to hold gun stock to strap rifle to side of pack, make waist belt a little wider (i like a good sturdy 3" strap as belt).