Garmin
Forerunner 255 Series
Long battery; but wrist HR tracking is inconsistent.

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Samsung Galaxy Watch 2018. Still working fine.
Sleep tracking worked on my original Galaxy Watch back in 2019 than my Apple Watch 11 haha
One thing I'll never understand as a user of the first Galaxy Watch Classic with its 7 day battery life is how for generations and generation of Samsung watch upgrades the battery life can only really last about a day. That crap is super annoying, especially when they want to charge such a massive premium when other companies are already using better battery technology and more efficient software to keep the watches going. This has been my frustration for years.
my galaxy watch 1 is still working fine since 2018. I'm planning to retire it this year.
I can't comment on Garmin watches, but does he already have an iWatch or a Samsung Galaxy watch? I track all my rides with my Galaxy watch with the strava app on it. Just food for thought. When I was looking at Garmin I was lookin at the Fenix models.
I am using Samsung Galaxy Watch that syncs with my Samsung Galaxy phone
Garmin
Forerunner 255 Series
Long battery; but wrist HR tracking is inconsistent.

Garmin
Forerunner 955 Series
Best value, clear MIP screen; limited smartwatch features.

Garmin
Fenix 7 Series
Durable, multi-week battery, flashlight; high price, buggy software.
Garmin
Instinct 2 Series
Rugged, solar multi-week battery; bulky, small screen readability issues.

Garmin
Enduro 3
Multi-week solar battery, lightweight; but bulky form factor.

Ranked #1
Oura - Oura Ring Series

Ranked #1
Apple - Ultra Series

Ranked #1
Garmin - Enduro 3

Ranked #1
Garmin - Fenix 7 Series

Ranked #1
Garmin - Forerunner 255 Series

Ranked #1
Oura - Oura Ring Series