Maybe I'm crazy, but I think I've had every single brand of base layer and there's frankly nothing that I would choose over my UA cold gear leggings/compression shirt.
UA changed the game in compressionwear 20+ years ago, and as soon as that transitioned into the hunting world, they revolutionized base layering as we know it. I really do think they're still the head of the class. I've been hunting over 20 years and have run entire marathons in their compression gear, and I don't have a single negative thing to say about them. I guess after about 50 washes, the gummy waist of the leggings can get a little wavy.
Now, every mid or outer layer that they sell that isn't goretex will suck water like a sponge and might not fit the best. As noted earlier, their sizing tends to be all over the place but their clothes are fairly indestructible. I shed hunt at least 100 miles a year in the northeast, in country that is loaded with multiflora rose thicket and dense brush - the UA will take that abuse when any of my Sitka stuff would shred like wet toilet paper. I beat it through miles of blackbear drives, days of farm work and season after season of whitetail hunting. It's durable. And warm (as long as it's dry).
But when it fails (and it will) - UA has always fully warranted everything that I've ever owned. Zippers break, hems come unsewn, colors fade, etc. Their website says that their logo is their warranty, and on numerous occasions, I've personally had them stand behind it.
If I had to put my life on the line in a backpacking situation, I'd trust their cold gear base layers above all others, but I'd lean toward the tech fabrics and heat-mapped gear offerings of the western companies for mid-outer layers.