I have Kuiu, Smartwool, FirstLite, Core4, Ice Breaker and Cabela's, and all of them are good. It really depends on the particular item of clothing as to which I like the best, but for most purposes, I like the Kuiu as well or better than any of them in the two weights of long underwear that Kuiu produces. Some of the heavier weight FirstLite and Icebreaker Merino clothing, like the sweaters and vests, are super-nice, but I don't wear them as much, preferring instead some lighter weight alternatives that are just as warm and can be compacted more for travel. I have seen the Ullfrotte, which seem to be really nice and warm too. There is some argument about where the best Merino wool is grown. Ullfrotte gets its wool from Patagonia, while Kuiu gets its wool from New Zealand or Australia. They both seem nice to me. In wool socks, I have used Smartwool, Lorpen and Cabela's socks. Again, all of them are nice, but I like the cut and construction of the Lorpen socks best. They are not 100% Merino, but they are great. I'm wearing a pair right now, as I do most days.
When I dress totally in wool for hunting, which normally only happens when I get to drive my truck to the hunting site, I love wearing Merino socks (with Merino liner socks if needed), Merino long underwear (sometimes two sets of different weight or a thin Merino sweater instead of the second top), perhaps a Pendleton wool shirt, a heavier (400 weight) Merino sweater or vest, and an outer wool shirt or jacket like the Shrew Longhunter shirt or one of the many nice Asbell shirts/jackets/Mackinaws (I like the new ones with the zippers for easier off/on and access to underlying layers and equipment).
Allan