I really like my Icebreaker merino wool tops as baselayers. The great thing about them is that they don't absorb body odors like my synthetic tops do. I even wear them in the early summer for that reason. I know I will get some back sweating from the pack and I don't want to stink so a short sleeve Icebreaker works great. As it gets on to high summer I switch back into synthetics because they wick a little better than wool.

As far as bottoms and midlayers I'm still experimenting.