Overall? Apple. Smart features and fitness tracking are great.
It's just a shame you have to at least be an iPhone user to even use it.
For fitness? Garmin. Hands down. Polar have a better app and I reckon their tracking and analysis are a bit better, but Polar's variety of tracking and smart features are severely lacking. Both have fantastic battery life.
Samsung are the best chocie for Android users, but especially if you are a Samsung user. The design, especially with the rotating bezel, is great. Bear in mind that their fitness tracking is dogshit though and has been for years. And while bringing more utility, the switch from Tizen to Wear OS tanked efficiency (and therefore battery life).
The rest are meh. I have a Fossil Gen 5. It randomly suddenly lags a lot, making it unreliable. No wonder Fossil bailed.