I found the runners more of a challenge than the clickers.
Clickers were strong, but they're not that hard to sneak past. Runners would always spot me if I wasn't really careful. So even though they're weaker, they need to be handled more carefully. If one spots you, you're in a bit of a pickle.
Clickers are scary when you don't have shivs. One hit kill I love it. Runners are pretty devastating as well. I can't wait for the stalkers, the way they are described will surely make me poop my pants.