I have both merino wool and synthetic base layers, but I prefer merino wool mostly because it doesn't stink anywhere near as much and dries easier, as long as it's not a super thin weave. I think just like any other material, there is variation between merino wool garments - different thicknesses, fit, weave, % wool, etc. My favourite is my Capo merino wool polo. Looks good on and off the bike, and feels comfortable. I usually keep the synthetic layers for more temperature days where it's warm enough that I don't mind wind drying off my sweat.