I'm looking at a September hike of the Border Route Trail and temps are falling then. Avg low by the end of the month is 35. I'm trying to decide synthetic or merino base layer. I'd like to hear your thoughts. I have a stack of short sleeve Under Armor/Columbia tech fabric shirts so I'd have to acquire a merino one. I looking at Ibex Woolie 150 crew or Indie Hoodie as examples.
Ibex makes lovely stuff, really top-flight. As to which is "better" there's limitless debate. Many, but not all synthetics transport sweat better and dry faster than wool. Wool tends to not stink after a few days while some synthetics acquire an aroma that can't adequately be described. Also, there's how well top layers glide over the base layer and how they feel against the skin and how they feel when you're overheating (e.g., climbing a steep hill in full sunlight).
No wrong answers, really, it's more a matter of preference as eithr adds needed warmth. It's what they do when pressed to the limits that separates them.