Is a heated top or heated bottom more useful for skiing?

For most skiers, a heated top provides more perceived benefit because warming the core (especially the lower back/kidney area) has a greater impact on overall comfort than warming the legs. The core is where your body prioritizes heat retention, and warming it signals to your brain that you're warm overall. Heated bottoms are worth it if you specifically suffer from cold thighs or have poor leg circulation, but start with a heated top if you're only buying one piece.