I have the Gear S2 Classic and AW S2.
Gear S2 Classic Pros ....
Design ... feels like you're wearing an actually watch.
Better and Brighter display.
Better Default and endless 3rd Party Watch faces.
Automatic Sleep record
Widgets
More Rugged
Compatible with tons of Android Phones and now iPhone.
Apple Watch Pros ....
Lighter weight
App integration is top notch and makes this the most functional smart watch, PERIOD!!!!
Force Touch. I actually use force touch on the AW more than on the iPhone.
Much stronger vibration.
Calls and iMessage without the iPhone when connected to wifi.
Siri
Better Water Resistant
I like both watches equally for differ reasons.
The option to wear my Gear S2 Classic with the iPhone is nice for occasion, but it's still not seamless enough yet, you still have to keep the Gear App open in the background. I wouldn't advise anyone to get anything but an Apple Watch for the iPhone. For Android, Gear watches are the best, as I dislike Android Wear.