Right now, I'd say Pebble. Samsung has the most "look, ma!" features, but the day-to-day utility isn't that great. They only play nicely with certain apps, and you can only use a subset of Samsung phones with them. Pebble works with Android and iOS, and it's not picky about apps. It's also cheaper and lasts longer on a charge, even next to the Gear 2 and Gear Fit.
With that said, it feels like we're at the same stage in smartwatches that MP3 players were at just before the iPod. There's some nice enough options out there, but you get the nagging feeling that the next generation will completely outclass them.