My go-to shirt right now is the RR Adventure top. It's very comfortable, very airy, dries fast, easy to wash, and looks great. I felt like a million bucks in the AT recently while wearing it.
I also have the Bone Flats, which I've trained in extensively. The material is much lighter but interestingly enough, this causes a better drape against the skin which results in a more clammy feel. In contrast, the Adventure top is barely heavier and seems to allow for better ventilation.