I've owned them all, I think. Stuck with the core4 merino base layers, I like the looser fit and have long arms and kuiu merino sleeves were to short. The core4 merino is the smoothest next to the skin out of all of em. But, I heard core4 was sold so that might not be the case anymore.
I have both the sitka ascent pants and kuiu attack pant, attack pant is better quality, period. Its warmer when its cold and cooler when its hot. Tough as nails, unlike the sitka that blew the seat out in a month. They patched the holes and fixed the blown out crotch but I had to pay for it... so much for a warranty.
I have two Sitka kelvin jackets that I bought on sale so I have not bothered with anyone elses primaloft jackets. I also have one of the kelvin vests that I bought on sale. I like this primaloft stuff.
I have some of the old kuiu chugach raingear and it puts any goretex outfit to shame, in my opinion.
Good Luck!