Lightweight waterproof rain pants are the more flexible default. They pack small, fit over different insulating layers, dry quickly, and are less likely to leave you overheating on an active landing. Some operator activities prefer them because fitted ski pants get in the way of safety equipment. Insulated ski pants work too, if they are truly waterproof, clear the boots and don't restrict movement.
There's no universal winner. The better approach is one waterproof outer pant with your warmth controlled by the layers underneath, rather than two heavy pairs. A thin shell plus thermal leggings plus an optional fleece layer gives you the widest temperature range for the least luggage.
If you already own proven ski pants and you run cold, use them. Just check they fit over tall rubber boots before you fly.