I normally do half a week of each. As mentioned, 6 day rental for snowboarding is normally slightly higher than for skiiing. I booked the 6 days snowboarding at Hunters last year and they let me change to skis without further charge. If it was the other way round though I'd expect to pay a small charge, but thats not confirmed. Didn't go with the ski package from my tour operator as they couldn't confirm they would do this half and half deal.