Polyester fleece is honestly the sweet spot for most resort skiers. It gives you solid warmth without a lot of bulk, dries fast if you work up a sweat, and holds up well season after season. Plus, it's typically the most budget-friendly option, so you're getting great value.
The main tradeoff is odor—polyester doesn't naturally fight bacteria like merino wool does, so after a few days of hard skiing, your balaclava will let you know it's time for a wash. If you're doing multi-day backcountry trips without laundry access, that's where merino shines. But for day trips at the resort where you can toss it in the wash between sessions, fleece is perfectly fine.
One thing to keep in mind: fleece alone doesn't block wind particularly well. On brutally cold, windy lift rides, you might feel it cutting through unless your jacket hood covers it. For those conditions, a windstopper or hybrid design would be warmer, but for typical cold and dry resort days, fleece gets the job done comfortably.