If you just want to use the built in fitness app and don't want loads of data, then the AW will be fine.
My primary use for my watch has always been fitness tracking and while I wouldn't say I was anywhere near a serious runner (I run nearly every day but just for pleasure), I do take my running seriously and like looking at stats and data about my runs, which is why I was using 3rd party apps (tried Strava, Runtastic, Runkeeper and many others). However, I found 3rd party apps to be horrendously unreliable (failing to start, failing to keep running, crashing, missing bits of runs off, etc, etc.).
After putting up with poor quality apps for 18 months I finally gave up and got myself a Garmin Forerunner 235 and I much prefer it as a running watch: It's rock solid reliable and gives me all the data I could ever want
As a watch, it's nowhere near as good as the AW (bigger, not as well built, not as good a display, notifications aren't interactive), but I'm happy to make the compromise on those and am now wearing it as my all day watch simply because it works better as a fitness device.
My personal view is if you want a nice watch that will also track your activities, then get the AW. If you want a watch to help you with your running and whose primary focus is fitness, then you may be better off with an alternative