I too am a merino fan – I have merino and a variety of manmade.
On really hot days, I think my manmade handles sweat better (but it may also be that the manmade tops I wear in hot conditions are more ‘lightweight’ and summer specific.
For 80% of the year, merino is more comfortable, maintains a steadier ‘core’ temperature, is much more comfortable when damp/wet (great for paddling/wet weather). I think its like soft shell stuff vs hardshell – at the ‘extreme’ end of performance its not *quite* as good – but for 80%+ of the time it is superior and more comfortable.
I now get trade discount for work on a brand of merino, and hope to open another when I start with another company for the staff and I… 🙂