Best synthetic I’ve used (by far) is the Altura Thermocool. Thin, dries fast, very warm for the amount of fabric it uses – really effective. Feels right in a wide range of temps.
Merino has to be the biggest ‘con’ for sportswear – unless you like cold, clammy baselayers?
[quote]I too was sucked into the merino myth and tried a few makes. They are fine for walking but no use for my sweaty self when cycling and I returned to synth. [/quote]
Merino is like Goretex in that it’s great for some uses and rubbish for others. If you can ride at a pace where you’re not sweating much (ie base miles or proper cold winter riding where being sweaty means a real chill), it’s fantastic stuff. If you’re going to be wet for a long period it’s also great. For sweaty types or high intensity, or needing a fast-drying layer in mixed conditions, forget it.