I'm commuting, so not actually wearing a 'base' layer but need a top to cycle in. I tried my cotton t-shirts (which are absolutely great for normal wear) but I come out in a light 'glow' which means they get damp which is not great.
I then bought a synthetic thing (not cycling specific, but should have worked). Colours great, promises wicking etc, which it did - unfortunately it also made me a teeny bit smelly
(which I'm not normally, but wearing *some* synthetic clothes does make me smelly), which then got wicked all over the shirt. Net result, I could have used it as a biological weapon.
The entire thing smelt.
After that I decided to try the merino thing after reading some glowing reviews. I am glad to report that I can wear the merino top all week (10 miles each way) and so far no smell problems. It's also been washed once in the machine - on a wool cycle but not using special wool detergent (but I normally use mild non-bio detergent anyway) and survived unharmed & unshrunk.
However, if you do get the 'base layer' or 'summer' merino styles, the weight of the fabric is similar to lightweight cotton jersey so the wind does cut right through it. Hence better as a base layer in the wind rather than an only layer....