Synthetic insulation like Primaloft, Thinsulate, or Coreloft is the most versatile choice for most skiers and snowboarders. The biggest advantage is that it keeps your hands warm even if the gloves get damp—whether from sweat, snow, or wet conditions—which makes it ideal for coastal mountains, spring skiing, or anyone who runs hot on the hill.
The trade-off is that synthetic is slightly bulkier than down for the same warmth level, so your gloves may feel a bit less low-profile. But that's a small price to pay for reliability. Synthetic gloves are also easier to wash and maintain, and they dry faster at the end of the day.
If you ride mostly in wet climates or do high-output activities like touring where you'll sweat, synthetic is the smart pick. Down is warmer per gram but loses its insulating ability when wet, so save that for dry, bitter-cold days.