Medium cushion is the most popular option for a reason—it strikes a great balance between comfort and performance for most recreational skiers. You get moderate padding throughout the sock with extra cushioning in high-impact zones like the shin and heel, which helps reduce fatigue on long days without making your boots feel overly tight.
This level works best if your boots have an average fit—not race-tight, but not loose either. It provides enough warmth for typical winter conditions and enough padding to take the edge off hard landings and long groomer runs.
The one tradeoff is that you'll lose a bit of that responsive, connected feel compared to thinner socks. But for most all-mountain and resort skiers, that slight reduction in boot feel is well worth the all-day comfort. If you're not racing or dealing with extremely tight or loose boots, medium cushion is usually the way to go.