There are as many opinions as there are feet,

I prefer polypropylene liners with Merino wool over them for several reason

The separate liners (not just a synthetic portion/mix of the hiking sock) provides a mechanical/physical sliding layer. This protects the skin better, whether wet or dry. You can think of this layer as being like moleskin.

That separate layer “lifts and separates” the moistness into the thicker spongy main sock where it can be dissipated. It always amazes me how effective this is when I go from a high humidity climate like my VA mts, to a low humidity area like the Sierra. My feet stay dry in the Sierra.

For those of us us with oddball size feet, surgery, deformities, ill-fitting boots, worn or sideways warped uppers, one can add (or subtract) one of those polypropylene or other preferred synthetic layers., using sock combinations to insure the fit. I know, I know, someone will say just get boots that fit. Nope. Not always possible.