I should preface my thoughts about the Apple Watch by saying that last night I drove to "Big Mac" (i.e. McPherson Avenue) for an evening run and ended up running into a group of runners from the local Running Room run club--they graciously allowed me to join them.
As always I used Runtastic, but this time I used the "Workout" app on Apple Watch to track my run. Aside from keeping a constant lock on my heart rate (and thereby producing what I think is a more conclusive calorie burn), the app also provided a few interesting post-run metrics (splits, distance etc.). Where the Workout app falls short is that it doesn't provide any maps or location data (not to say this information is not recorded), which happens to be something about Runtastic that I really like.
But the utility of the Apple Watch is in the fact that you can leave your phone zipped away. This is a big deal if you're running during a Canadian winter--phones have a habit of freezing when it's cold enough. Since the Apple Watch will allow you to control both Workout and Runtastic apps, you really don't need to take your phone out. The watch is also in contact with your skin, which produces heat, and this helps the watch to avoid freezing. Last night's run was in the -15C to -18C range, so I'm impressed that the watch held up over the six kilometre distance.