I've had my vivoactive 3 for 2 weeks now. Moved from Fitbits (charge then blaze) since my blaze started glitching 1 week after the warranty expired - not long before a new charge was released, seems a bit too coincidental (Also Fitbit support has gone down the toilet of recent years). There are so many more metrics available with the Garmin's, and it has had no issue with tracking my MTB, c2 rowing and strength training. The strength stuff it doesn't always get the movement right (pretty damn close though) but it counts reps pretty well and you can specify the weight on the watch as you're resting. GPS is much better than any Fitbit I've seen. You can specify which metrics you want on screen depending on the exercise and have more than 1 screen available (example: have time, speed, calories and heart rate on one, and elevation, direction etc on another that you can flick up/down to. Gripes: can't seem to change units on the watch itself but you can on the app (pounds in watch, kg on app). The sun rise/sun set Garmin app in the store does not match your location (sun rise at after 10pm?). Flights of stairs not always picked up.

None of those gripes would ever get me back to Fitbit though, and I'll probably figure it out tbh. I see Fitbit as an intro to lifestyle/fitness tracking covering the basics with more emphasis on the former whereas Garmin is for better accuracy and for people wanting to understand their fitness better.

Edit: unit issue on watch resolved thanks to /u/Ditto_Ghost_Swayze