This is actually a tough question because a lot of it depends on the dog.
When we were first designing the Runner's Choice we looked at a lot of canicross and skijoring equipment, including the harnesses. What we came to understand is those types of harnesses actually encourage dogs to pull. At that time, our dog was just turning one. We were just starting to introduce running to her, and we thought that we would use a x-back style harness for running and just her regular collar for walks. It turns out our dog LOVES to run, and needed no encouragement for running ahead. For her case, we actually needed to slow her down. We've ended up running just using a collar, except when she is overly excited. When she's like that, we use a head harness. It slows her down just enough that she isn't pulling us out of good running position.
We have read criticism about the front attaching harnesses and running. We believe that the ones that are being debated are designed to collapse forward when a dog pulls. Some vets argue that dogs are built to run with their weight forward, so that style of harness encourages them to go light in the front shifting their weight backwards.
Bottom line - If your dog isn't a huge puller, then a collar or a harness that doesn't collapse when a dog pulls will probably work just fine. If you need to do something to prevent pulling, we have had good luck with the head halter. On the other end of the spectrum, if your dog needs some encouragement to run it appears as if the x-back harness helps.