I did my first run today with the AW and Fenix3, with AW results all over the place.
I started the run with using the Workout app. This was my usual 8 mile route, so I (and my fenix) know the mile splits well. At 3.1 miles, the AW Workout app had 2.70 miles. I stopped running, completed and shut down the Workout app.
Next I started the Strava app on the AW in running mode for the next .9 mile. Complete garbage. Pace was OK, but no distance was displayed on the screen. At the end of .9 mile (4 miles total for the run), I stopped running and stopped the Strava app. It had that segment as .2 miles.
At this point I was half way through my 8 mile run. I started up MapMyRun on the AW. For the next 4 miles MapMyRun and the fenix were nearly identical, and at the end of the final 4 miles of my run they were .01 different.
As everyone has said, the AW and the Workout app need time to calibrate. Although, I really don't understand why. If MapMyRun can get it right the 1st time (using the same GPS), what calibration is the Workout app doing??? I know some suggest that the Workout app is more stride and cadence based rather than GPS based. If so, is this for battery performance reasons.
Again, the need for calibration seems very strange. I've run with GPS watches for many, many years, and I don't recall ever having to calibrate them. I am aware that GPS accuracy is dependent on the software (along with settings and signal), and that GPS accuracy can vary from watch to watch, and across software/firmware versions for individual watches.
In any case, tomorrow I will try to stick with the workout app and let it continue to learn to see if gets closer to real life accuracy.