Garmin
Forerunner 255 Series
Long battery; but wrist HR tracking is inconsistent.
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I don't think you'd want to go with mine. It's a [Forrunner 735XT](https://www.garmin.com/en-US/p/541225/), which is an older model that's been discontinued. You could probably find it used, and it's certainly a solid watch, but the technology has improved drastically in the years since I bought it.
Mine finally gave out a few weeks ago. I just got a fenix 8 47mm amoled. I had the 735xt for 7 years and the screen started to flicker during activities and it’s now unusable.
I liked the simplicity of the 735xt. I didn't really feel it on my wrist, it was light, and didn't get in the way. The fenix 8 is a very different watch. It's much larger and heavier and I find that I think about it more often, which i don't like. I do really like the additional features that the fenix has, like the sleep tracking and hrv measurements.
The difference won't be that big probably. Up until last week I ran with a 10ish year old Forerunner 735XT and it was still super capable with easy ~1week+ of battery life.
Had a forerunner 735xt since 2018, sadly it died 2 months ago but i was honestly thinking of going instinct 3, as it is 100 dollaridoos cheaper
I had a $20 vivo active 2 that was super simple. Wanted heart rate so I got a cheap Fitbit. Wanted better tracking and ability to use chest strap heart monitor, so i got a used forerunner 735xt. Fitbit wanted a subscription to see most of the data. Garmin cost more but didn't require subscription. It worked good enough but was aged technology. Got a good deal on a used 955($200 used). It's a MIP screen and I order it over newer OLED screens.
Glad it helped. I should say thin in terms of men’s watches. 18mm seems pretty normal for a women’s watch, but it would be nice if they shipped the small watch with the big band as it’s easier to size down instead of up. You can’t put a 20 on 18mm lugs for example. There are other watches from polar and coros, but I’ve never found them terribly compelling. Again, I just want like a 40-42mm case with a 20mm band and a few other features, and sometimes it’s hard to find. Edit, if you can find a garmin from a few years ago, go for it. I have a 735 and it’s a good watch for sports, but it falls behind in music storage and smart watch capabilities. It’s light and the battery lasts forever though.
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.

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Oura - Oura Ring Series

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Apple - Ultra Series

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Garmin - Enduro 3

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Garmin - Fenix 7 Series

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Garmin - Forerunner 255 Series

Ranked #1
Oura - Oura Ring Series