If you’re an iPhone user, the best smart watch you can buy is an Apple Watch - there’s no contest.
Pair it with the Athlytic app and you’ll have a reasonable sensible whoop-like Daily Recovery score along with nice presentation for lots of other health and exercise metrics, that pulls all its data from Apple Health.
Given that last point, you can also use it with Garmin etc if you’re syncing to Apple Health, but given that the Garmin is a terrible smart watch when paired with an iPhone, that’d be a waste!