I bought all Sitka, sold it all and bought all Kuiu, basically playing "fanboy" and chasing 'flage patterns. I finally decided to sell all my kuiu and move to solids as I have no problem wearing it hunting and can also wear it casually or for matches. Here is my breakdown of what I think are the best of each
Pants:
Overall: Sitka Timberline, light and breathable, reinforced knee and butt is awesome and removeable knee pads nice touch. They can be a little warm early season or on long hikes.
Early season: I prefer the Kuiu Attack pants, seem to hold up really well, the hip zips are great for dumping heat on hikes or during early season hunting.
Rain: Probably a toss-up between top offerings of Sitka and KUIU, I have the Chugach but sold it and now own Sitka Stormfront, they are a little heavier but bombproof with gore-tex and have held up during matches in the rain rolling around.
Baselayers: First Lite, just universally accepted as some of the best, they have some zip-off options that are interesting.
Tops:
Overall: Sitka Jetstream, the single biggest factor is the Gore Windstopper layer in it, I had the Kuiu Guide and felt like wind went right through it, the Jetstream is my go to jacket on almost every hunt. Has plenty of pockets, hood, pit zips, slightly longer in the rear, and quiet, put on plenty of stalks wearing it and no issues.
Early Season: Take your pick, Sitka has some nice pieces, if you want merino look at first lite, or Kuiu has some thinner Peleton layers. I wear a Lightweight Sitka long sleeve t shirt, and if it gets a little chilly will put on a heavyweight hoody shirt.
Rain: Look at Pants
Baselayers: See Pants section
Gloves: Owned quite a few of them, my favorite for glassing right now are the First Lite Grizzly 2.0 mitts, super warm, enough dexterity to use my binos or spotting scope, leases to not lose them and removable liners. My day to day favorite are a pair of Arc'teryx that have held up amazingly well, they have a very thin layer of insulation to take the chill off, they have touch fingers so I can still use my phone withe them on, no velcro to get hung up or cause noise, not sure if they make them anymore but hope I can find another pair as these are money.
Socks: I really like my First Lite socks, have held up really well, do not seem to get a ton of smell even after long days wearing them, I have not tried GORE or Kuiu but do plan to buy a couple more pairs of First lite.
Insulation:
This is a tough one as it completely depends on how you plan to use it and what your conditions will be like. I had a kuiu super down and had no complaints, it seemed super warm whenever I wore it, I sold it to not have camo and bought a First Lite Brooks, it is thinner and not quite as warm but that has been okay for me as I usually did not need the extreme heat the Super down provided. Another factor is if you will be in wet areas, sometimes you need to look synthetic so it can dry out, if its natural down and gets wet you are SOL, some are DWR treated but not sure on longevity of it.
Biggest downside to First Lite and Kuiu is that you cannot try them on, but I usually just order a couple extra sizes and then decide which fits best. If you have friends that wear it see if you can try on a couple pieces and get a sense of what your average size is.