For me, running is harder. Although I was a pretty successful runner(sponsored by a shoe company and successful at distances from 5k to the marathon), I absolutely hated hills. I never stopped to walk up a hill but that's not to say that I didn't slow down to a crawl! But on the bike, I love climbing. For some reason, it just seems so much easier to me. When running up a steep incline or long steady climb, I would think, "Gosh...this really sucks." But on the bike, I am sometimes sad when the hill is over.