The power band is great, but only if you are in it.
a two stroke will give you power that is proportional to the twist of the throttle, but the "gain" function will change dramatically over the RPM range.
A four stroke will give you much more predictable power over its RPM range.
If you have the appropriate skill a two stroke can really shine. If you are beginner and have trouble attacking the hill at a rate that will keep you in the power band you will be a lot better off on a four stroke.
Rod