The data available on the AW is very good and if you have an iPhone it just works very well with it.
Have had a basic garmin before, was great but the integration with phone and watch is nowewhere near as good as it would be on the AW.
The health data, including ECG and o2, etc. also seems to work very well.
DC Rainmaker has tested accuracy of various watches vs. each other and although I read it some time back, from what I remember the AW was highly accurate in terms of heart rate; he compared it to a device with a strap.