A smooth tire would be easier to roll. A good, cheap (though not light at 920g) option is the CST Cyclops 2.4. I have one on a 24" wheel for cruising and like it very much. If I was buying a tire specifically for a hillclimb I might be inclined to give up some volume for a lighter tire. Maybe something like a Tioga PowerBlock 2.1 (520g).