An Apple watch would be the obvious choice. I have a much cheaper Fitbit tracker, but I wouldn't recommend it. The model I have (Charge 3) has a pretty poor HR sensor (often reads way too low during exercise when sweating) and the display is impossible to read in bright daylight. HRV function is also next to useless. I'm not sure how much better the Apple watch would be in this regard, but it can't be any worse.
If I was buying this primarily for sports use, I would probably research the latest Polar and Garmin products. My Polar optical HRM which I wear as an armband and connect to my Garmin head unit is excellent. But if this was for general use as an everyday watch, then I would probably just get an Apple watch and pair it with my iPhone.