I have used fitness trackers for about 5 years. I went from Jawbones/Fitbits/Vivoactive 3/Suunto S7 and finally to my current Fenix 6s Pro. I have used it for about a year. Here is my experience with the Fenix 6s Pro.
My use case for a fitness tracker is the following: I'm a middle aged guy. I'm gearing up for a half marathon/full marathon. I golf a couple of times a week. So I needed a watch that had good battery life and GPS capabilities. I'm also concerned about my health so I like lots of health stats.
I had a Vivoactive 3 and this was a good watch that fit many of my needs. My only two gripes were it's battery life (it would last about 4~5 hours with the GPS on). And the touchscreen was a giant pain in the butt - it would sometimes move from hole-to-hole in the middle of golfing. I went to the Suunto 7 in the giant 'dream' that Suunto put together the true smartwatch/sportwatch. Nope, I sent it back within 3 days. I finally settled for the Fenix 6s Pro.
In regards to my two main use cases: golfing and running - The Fenix 6S Pro has been outstanding. All of my runs have been tracked properly. There has not been any diversions and the accuracy is consistent. For golfing, all of the courses are on the watch (no downloading), and again the accuracy has been great. I track all of my shots/scores and analyze after the round. Very good. Finally this is the first watch that I have had that doesn't have any nicks or scratches. This watch is tough.
I realize that other here have had issues (WHR, GPS, etc.), but if you need a watch that is good for non-competitive stuff (like running and golf), I would definitely recommend it.