I'm sure some of you know this. But for those who don't here is some general information on how this stuff is supposed to work:

Polypropylene is the most hydrophobic synthetic material commonly used in athletic clothing. It also has a low re-activity to most chemicals, UV light and electricity. On a microscopic level the individual fibers are fine but solid. As a base layer it works by fitting close to the skin where it's hydrophobic properties force sweat away so it doesn't evaporate on the skin which would pull heat out of your body. The 'stink' factor is created by it's non porous oleophilic nature which which attracts body oils and dirt to it's surface and creates a breeding ground for bacteria. Most of this is also true for polyester, but to a lesser extent depending on exact make up and treatments.

Merino wool is the most hydrophobic natural material commonly used for athletic clothing, although it is not as hydrophobic or unreactive as polypropylene. It does have textured, spring like fibers (think fusilli pasta), though, that use capillary action to pull moisture away from skin. They also due double duty by holding their shape even when wet which is why wool is still a good insulator when wet. But merino does not generally dry as fast as polypropylene of the same fabric weight due to the shape holding a bit of that water. Wool does have natural anti-microbial property which tends to keep BO down.

Cotton is hydrophilic. When in contact with water it soaks it up and tends to hold it taking a long try to dry. This also causes it's structure to collapse and loose it's insulating properties.

But that said, there are a myriad of different people and riding conditions. So try some of this stuff yourself. As I said earlier, I personally like wool as long as I am not wearing a highly wind resistant outer layer. But if conditions warrant using a windproof jacket I switch to a thin, body fit synthetic base and then layer in between as needed.