What is more important to consider when buying a flashlight the candlepower or lumens?

They are one in the same just a different way of measuring the output of light. Much in the same way one would say a football field is 100 yards long it is also 300 ft. A rough answer to your question is 100 llumens equals about 26,500 candlepower. The term candlepower came about of course way back when everyone used candles in stead of modern lightbulbs. Llumens come from putting light on an object from a distance and maesuring the light at that point and distance. Very similar is horsepower and torque where horsepower is NOT a measured number on a dyno it is computed from torque output then converted from work over time.