I've been using smart watches for 3 years, had both Samsung and Apple watches, and I enjoyed using both.
I probably would've stayed with the Apple Watch, but Samsung's watches and accompanying health app had some features I didn't find on the Apple Watch like automatic workout detection, automatic sleep tracking, which provides a graph and chart of Awake, Light, Deep, and REM sleep phases, and a pedometer--the latter two I had to find and download apps for the Apple Watch.
Currently I have the Samsung Watch Active 4, which is a big improvement over the previous Watch 3. But Apple has a gang of new features coming for their watches with their announcement of Watch OS 9, which will bring some of those missing features I mentioned.
The Apple Watch and the Android-based Samsung Galaxy Watch are the top 2 watches on the market now, both are good. If you have an iPhone, I'd say start with a Apple Watch 3, the cheapest one Apple has, or the Galaxy Watch Active 4, if you have a Samsung phone or any android phone.