I bought into the Bangle.js 2 Kickstarter and I have to say, I'm incredibly happy with it. Granted, I've done nothing with it besides design my own watch face and take advantage of the GPS to set the time occasionally, but I know it's capable of a lot more. It was very easy to write the watch face code, and I feel like it would be pretty easy to do whatever I wanted to do. Ecosystem for it is probably a bit more developed than it was at launch, too- they were supposed to follow up with some apps that made interfacing it with your phone easier, dunno where that ended up.
To be fair- I've also got PineTime bookmarked for if my Bangle.js 2 ever breaks, or I just want to mess around with some lower-level aspects of watch firmware.