Either yarn
The same three sweaters are knitted in either. The cashmere is the goat's winter undercoat, combed out by hand in the spring as the animal begins to shed it, which is work done a goat at a time and is most of why the fibre costs what it does. The merino is shorn, extrafine, and spun in Biella. Both are two ply and both are fine -- Nm 2/28 and Nm 2/30, which is fourteen and fifteen metres of yarn to the gram -- so a single sweater holds something near six kilometres of it. Cashmere is warmer for its weight and softer at the neck; merino holds its shape longer and takes harder wear. Neither is the better yarn. They are for different winters.