The Pebble watch will work with both Android and iOS, for starters (but then again, so does Android Wear devices now too... leaving just the Apple Watch to only support Apple products).
It's SDK is in Python or C, and it makes it really easy to write up basic apps for yourself or others (no special hardware, licenses, or fees necessary to start developing your own apps).
Battery life kills all other smart watches. The always on screen is very nice too (makes it usable as an actual watch, for instance).
So called "Smart Straps" allowing 3rd parties or the OEM to produce different wrist straps capable of different functionality (sensors, additional battery, etc...) - And they are swappable/upgradable.
Even for non-developers, it's easy to create watchfaces using http://www.watchface-generator.de/. Upload a photo, customize your text and download the app to your watch (credit to Paul Rode, a 3rd party developer for this)
It's SDK is in Python or C, and it makes it really easy to write up basic apps for yourself or others (no special hardware, licenses, or fees necessary to start developing your own apps).
Battery life kills all other smart watches. The always on screen is very nice too (makes it usable as an actual watch, for instance).
So called "Smart Straps" allowing 3rd parties or the OEM to produce different wrist straps capable of different functionality (sensors, additional battery, etc...) - And they are swappable/upgradable.