Since I got one of the original Pebbles which came out as a Kickstarter project I've been interested in the smart watch movement. Pebble did a lot of things really well (which I'll look at shortly) despite the limitations placed upon them by the platform I was interested in (iOS). Since then (and probably prior to as well) there have been a slew of different devices which integrate with your phone. Broadly I think these fit into a couple of categories: fitness tracking, and phone interaction.
I haven't tried many of these because a) they're all reasonably expensive; and b) there are only so many limbs to comfortably attach devices to for the period of time necessary to form an opinion about them. The devices I've tried have been the Fitbit Flex, original Pebble, and the Garmin VivoSmart. The Fitbit and VivoSmart are both firmly in the fitness tracker camp with the VivoSmart bolting on some interaction features, whereas the Pebble is definitely aimed at interaction with the phone with fitness features bolted on with apps.
In the filter bubbles that I travel in, I feel that the Pebble gets a really bad rep. The Apple camp (the John Grubers and Marco Arments of the world) knock the Pebble because they think it's ugly. To a certain extent they're right, it's not a dress watch by any stretch of the imagination. It's utilitarian, relatively bulky and made of cheap materials. The trouble is I don't think that argument really sticks. Look at all the fitness tracking stuff that people put on their wrists and you'll see a host of other bulky, utilitarian and cheap devices which no one complains about. The reason you wear them is not to be fashionable, it's because they do something for you. If they could look better while doing it then all well and good, but for the most part they're there as part of the furniture.
I've been trying to get back into running in the mornings (with mixed success, but that's another story), and I thought I'd take advantage of a local sale to get one device to replace my Fitbit and Pebble, and bought a Garmin VivoSmart, which is a fitness tracker but combines a bunch of the watch and remote control functions that I use a lot in my Pebble. The VivoSmart does a few things really well, namely the fitness tracking stuff, but does a terrible job at any of the other functions: it has a terrible low resolution display which is next to impossible to see in bright sunlight, the tap sensing is inaccurate and frequently requires some pretty forceful taps to show the display (which my students found hilarious), configuration of the device has to be done on the companion app, and the advertised music remote control doesn't work at all (feedback I had read beforehand suggested that it only worked with the Music app, but I couldn't even get it to work with that).
Notifications were another poorly implemented aspect of the VivoSmart. The vibration on the wrist was about the same as the Pebble, but the timeout on the display was so brief that by the time I got to look at your wrist (or shaded it enough if outside) the message would be gone, and I'd have to wake the band up, go into the notification section, find the message and then scroll through it to read it. In other words it might as well not have bothered displaying it at all and just done to buzz to let me know to take the phone out.
TL/DR, don't buy a VivoSmart if you want anything more than the tracking functions.
So I went back to my Pebble. I have missed the remote control functions even more than I thought I would. The Pebble with play/pause/skip just about anything you want it to, with the slight problem of it occasionally losing track of what has been playing (might have something to do with reconnecting after going out of range of Bluetooth). One of the beautiful things about having hardware buttons on the Pebble is this means you can control playback while driving very easily without having to look away from the road. When you're in the music control interface, you're there. You don't have to wake the watch up, reactivate that set of controls and so on as had to happen with the VivoSmart (not that it worked anyway), you just hit a button and it plays, pauses or skips. This is one feature that I think is superior to that way that I understand the Apple Watch works, since the display will turn itself off to save power, although I'm unsure of whether you need to interact with the UI to get into playback controls and so don't know how well it functions as an eyes-free device.
After I started drafting this post, I got an email from Pebble advertising a new round design (literally called Pebble Round *rolls eyes*) which is starting to look more like a fashion watch. They sacrifice five advertised days of battery life to do it, which is a little disappointing. One of the nice points about the Pebbles so far has been that you forget about the juice in them until they remind you that they're low, as opposed to something you need to always think about charging.
One the battery front, I backed another Kickstarter project ages ago called the Moment Smartwatch which was a design incorporating a curved eInk display which went all around the wrist like a bracelet. They also advertised packing about a month's worth of battery in it which would have been awesome. Sadly as time goes by it's looking more and more like vaporware, despite infrequent updates. Also I'm unsure of whether I'd actually wear it, since it looks a lot like jewellery, but then I've never been one to care much about what I wear.
 - I wish Pebble would get their branding mojo back. "Pebble" is a great name, but their "steel", "time" and "round" names just stink.