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

Running these analyses costs money. Buy through my links to help keep lights on! I may get a small commission.
PW 3 is MUCH better than the OG. Sleep tracking works every single night. It charges much, much faster. The battery lasts longer. The UI is quicker. Apps update faster. Fitness tracking is more accurate.
I'm using the Pixel Watch 3 with Golf Pad and it works great.
I use a Pixel watch. Golf Pad (the app I use to track my rounds) is compatible with the watch.
When I switched from PW1 to PW3 41mm, it was like a day and night difference. Both in terms of UI responsiveness and battery life. I think you'll be happy if you get a good trade-in deal and discount.
I thought I would dislike daily changing, but I literally just charge it during my shower in the morning. Pixel watch 3.
Pixel watch 3 or 4. Both will last you comfortably more than 24h, especially the 4. Some of the best sensors and sleep tracking there is. A step down on health tracking but by no means bad is the oneplus watch 3. Much better battery life and tougher build.
Smartwatches aren't really medical devices, you should really consult with your doctor for advice in a proper monitoring device. That being said, if you have an android phone, pixel watches are hard to beat. Best heart rate sensors and continuous heart rate monitoring. ECG cannot be monitored passively as you need to close a circuit around your body, which means there's an electrode underneath the watch and the other is the crown, you must take spot readings with the opposite hand you're wearing it on.
The best sleep tracking outside of the oura and whoop are fitbit and pixel watches. If you want multi day battery life, it would need to be fitbit. Amazfit, garmin have great battery life and sports tracking, but mediocre sleep stage tracking.
I have experience with multiple Garmin watches and the Pixel Watch 3 but will both track sleep and health really well. The question is do you want A) a smart watch that integrates really well with your phone and can do cool things but has a shorter battery life, or need LTE or B) One that has less smart watch functions (but can still respond to texts and show messages) but only needs charged once a week or less and can track many walks or other activities during that time. I have a Venu 3 and really like the Garmin health tracking system and battery life, but also have a pixel watch 3 that I use for taking calls on runs and better interactions with my smart home setup. I've tested the sleep tracking on both and it's pretty similar.
Cool. Almost all Garmin models are Bluetooth/WiFi only. You'll get 2 free years of data and texting with a Pixel watch 3 or 4 LTE, but can cancel after, not activate it or buy the WiFi only version for a little cheaper. As far as subscriptions both Garmin and Fitbit offer subscriptions for AI workout recommendations and analysis but all regular health and sleep metrics are free. The Fitbit one has an instructor led workout component like peloton and Garmin is trying to be an all trails competitor but I've never paid for either and have never felt like I'm missing out.
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