I have had the opportunity to experience both watches I have utilized the Samsung Gear S (prefer the size of the Gear s)and also the Gear S2, and apple watch for about 7 months based off my experience each system/watch has both advantage and disadvantage.
The android smartwatch had the swype keyboard that worked great and google voice, the email app was faster opening an email including gmail, android watch had the sleep monitor automatically and DEFINITELY love the fact that the watches were capable making calls without the phone being in bluetooth range.Adding to that the watch would still get it's alerts like SMS, email, and calls, calls from the watch not being in range of the phone will automatically call from the watch number, same for incoming cal they are forward to the watch so you never miss a call. the health meter on the android watch provided a lot of info but in a simpler format, tons of watch faces to chose from, there are a few more but those were important for my usage.
Some of the apps could use some polishing they still look archaic, speaker could louder, size of the Gear S2 could be a little bigger (my big mitts make it look even smaller lol) like the moto 360.
APPLE I really like the app integration on the apple watch, APPLE PAY, the GPS with turn prompts via vibration, band swaps are a breeze, the ability choose between audio or text for sms. SIRI is better than S-voice!
CONS Wish they made a bigger face than 42mm, sim chip capability, sleep monitor, louder speaker, swype keyboard.
I currently am using the apple watch at this time and it does the job very well I am sure the next version I think will be sim chipped enabled (hopefully).