I have both open country and the whitetail patterns in Sitka. The only way I can justify it (i.e. afford it) is because my wife works for Gore (owns Sitka) and gets a pro deal for it. When I switched over to Sitka, I was amazed at the athletic fit, especially when hiking up steep slopes. I don't have to worry anymore about the crotch/thigh area binding on me when I start hiking uphill (you know what I mean). I use the open country in the lower elevation and whitetail pattern in the forest. I got the whitetail pattern before they came out with the new Alpine pattern (not switching). For base layering, I absolutely recommend the merino wool. First Lite, Helley Hansen, Minus 33, and others out there make great wool base layers. I'm seriously considering getting rid of all of my Under Armor to replace all of my base layers with either FL or HH merino wool. The different Sitka options give you good choices for a layering system for cold days. Granted, I'm not sitting in a tree-stand and am mostly moving, but those winter days where we're just sitting, glassing hillsides isn't much different.
As for high-end, athletic fit camo, Kuiu is another good brand.