The operating system you choose depends solely on the type of smartphone you have because the smart watch is paired with your smartphone. If you own an Android smartphone, your smart watch should have Android Wear or Tizen. If you own an iPhone, choose an Apple Watch. For example, the Samsung Gear S3 runs Tizen and is compatible with both the Android and iPhone.
The style offerings for smartwatches have improved dramatically, and your options are no longer limited to “large, nerdy and round” or “large, nerdy and square.” Still, even with more than 300 Fossil-branded watches planned across 14 major watch and fashion brands, smartwatches are generally much wider and chunkier than standard watches, as the size needed to accommodate the electronics and battery lends itself to bolder, more pronounced styles.
Fitbit Versa: The Fitbit is the health tracker for the masses and they have a model for every need. But the best option for adults who do a moderate amount of exercise and just want to keep tabs on their general fitness (ie: most of us), the Fitbit Versa is a great choice. It's an entry-level smartwatch. For more on the Fitbit Versa’s various attributes, read my in-depth review. ($350)
The top smartwatches that debuted at the 2017 Consumer Electronics Show included the Casio WSD-F20, Misfit Wearables Vapor and the Garmin Fenix 5 series. Apple released on September 22, 2017 their Apple Watch Series 3 model which offers built in LTE cellular connectivity allowing phone calls, messaging and data without relying on a nearby smartphone connection. 
Other reviewers also like the Q watches. Simon Hill at Digital Trends writes that the Q Explorist is “an attractive smartwatch to use with an Android phone that will blend in at work or play at an affordable price,” and that, aside from the Apple Watch and the Gear Sport (for Samsung phone owners), the Q Explorist “compares favorably with the rest of the field.” Gerald Lynch at TechRadar summarizes the Venture as “a sharp-looking, comfortable smartwatch with a great display and responsive processor,” but knocks it for lacking GPS and a heart-rate monitor. Matthew Miller at ZDNet believes the Explorist and Venture are “priced fairly for nice looking fashion watches that also serve as smartwatches.”
But your phone will play an important part if you do get a Fitbit or Garmin device with the aim of tracking your activity. It will be the place where your health data is synced to, you can tinker with your tracking settings and review your progress. There’s also a whole ecosystem of health apps that plug into tracking devices, combining them with exercise and diet advice - MyFitnessPal, Runtastic and Strava are three of the most popular ones worth checking out.
That’s the big downside of relying on your phone as a tracker, unless it is somewhere on your body, whenever you are moving about or exercising, all that effort won’t be counted. For some people - say joggers who wear their smartphone on an arm band, that’s not a big issue, but you really aren’t getting the full picture of your activity, including the things you do in your sleep, without having a gadget mounted on your wrist.
How frustrating. I really -like- the idea of a smart watch... but it's so hard to find the right one. I'm not an exercise freak so heartrate monitors etc are useless to me. I really like the design of the Samsung watches with their bezels to control it, but the Tizen OS with it's limited apps puts me right off. The Access Grayson watch is beautiful, but the lack of NFC is a deal breaker for me - Google Pay with the convenience of a watch is part of the reason I'd buy one. I don't need to be able to put a sim in it... that's what my phone's for, but GOS would be nice for when I travel, and as a motorbike rider some level of waterproofing is a must. Guess I'm waiting for the next round of watches to see what's on offer.