Base Layers: First Lite's merino wool is the best on the market from what I've seen and felt. Mine has been durable, comfortable, and does a nice job of moisture management. Meriwool is probably second best from what I've read, but I haven't gotten my hands on any.
Mid Layers: To me, mid layers matter the least from a brand standpoint. I don't see any reason to spend crazy money on one of the high-end brands' fleece or puffy when Eddie Bauer, Magellan (Academy's brand), and similar low-to-mid-cost brands produce mids that are VERY comparable. That said, the one piece of clothing that has made the absolute biggest difference in my comfort on stand is my Ororo Original Heated Vest. It's warm and comfortable even when it's turned off, and there's nothing like getting a consistent blast of heat to your core when you get a chill on you in the deer stand or duck blind. I put it on under a light outer layer as early as upper 50's and wear it through the end of duck season on every single hunt.
Outer Layers: I've been working on figuring this out this offseason. I have a Nomad outer jacket that I really like, but it's pretty heavy. I've bought or been gifted several First Lite outer layers (Solitude Bibs, Corrugate Foundry Pants, and Whitetail Catalyst Jacket), and I am returning every single one because they just don't fit me quite right (6'3, 165 lbs.). My dad has almost every piece in the Asio Gear lineup, and he swears by it. Seems well made and is definitely thoughtfully constructed with whitetail bowhunters in mind. I'm in the middle of researching what's the best outerwear system, and right now, I'm torn between the Sitka Stratus set and comparable offerings from Kuiu. I'm not especially hard on my gear--I take good care of it--but I ask a lot of it in terms of temperature ranges in which it's useful. I can't afford to buy three different Sitka/First Lite/Kuiu outerwear systems: one for sitting still in a freezing cold tree stand or duck blind, one for more moderate temps while sitting still, and one for run-n-gun turkey hunting on Tennessee spring mornings where it can be 30-60* on the same hunt.