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Can only second wool. Used to have really nasty sweat buildup in the past with cotton and the socks would be yellow and stinky after just a day, with merino I can wear the same pair several days before they even lightly smell. Even in peak summer thick wool socks are better even if it sounds counter-intuitive at first.
What also helps is walking barefoot more often (so that excess callus gets lost that way instead of ending up in the socks and fermenting there, and so that the toes can spread out more) plus having shoes that don't cramp the toes together, as this causes bad ventilation locally and friction leading to more callus buildup where you don't want it