Garmin
Forerunner 255 Series
Long battery, but wrist HR often inaccurate.

Running these analyses costs money. Buy through my links to help keep lights on! I may get a small commission.
>a lot of smartwatches had to be recharged every few hours, not just every day My Amazfit Bip had about 3 weeks of battery life, Amazfit GTS3 had 2 weeks, and the current Amazfit Bip 5 have 7 to 10 days.
Amazfit BIP was very nice. Still miss that MIP screen. Had BIP U Pro, T-rex Pro, T-rex 2 and their screen wasn't nice as BIP's MIP. And yes, Garmin is years ahead of Amazfit in terms of software..
I wouldn't use it for any scientific research. To be clear: I've never used it. I've used the Xiaomi S1 watch (high end), the Amazfit Bip, Band... something, and I have the Amazfit Band 9 Active right now to tide me over because the backlight on my Garmin Vivoactive 3 has died. (And because it cost 40myr delivered ($10usd)) The two bands - Bip have been dubiously accurate. Basically fine, I guess.
Kinda regretting getting the round early. I'm used to the square Bip and this feels sexy.
I sleep with my trex 3 pro (48mm) which is very bulky. I think that even though it is big, I progressed over the years from the mi Band 3, to amazfit bip, to GTR4 and then to this one. The progression makes it easier
Amazfit bip. Battery lasts 14ish days, does everything an Apple watch does and does the sports tracking. I love mine. I usually use the walking/hiking feature. I hit the start button for the workout and it let's me know when I've hit a mile, how long it takes me to do a mile etc. It can show where I've gone. The amazfit pro speaker is better than the bip when using the phone function. It does not come with cellular. It only has calls coming through with Bluetooth connection. But you can answer calls and talk over the phone using the watch.
Garmin
Forerunner 255 Series
Long battery, but wrist HR often inaccurate.

Garmin
Forerunner 955 Series
Endurance battery, value king, but clunky UI.

Garmin
Fenix 7 Series
Rugged, long battery, maps, but HR and software can struggle.

Garmin
Enduro 3
Unrivaled multi-week battery, solar-charged, but bulky.

Garmin
Forerunner 965
Lightweight, vibrant AMOLED, maps, but wrist HR and swim issues.

Ranked #1
Oura - Oura Ring Series

Ranked #1
Apple - Ultra Series

Ranked #1
Garmin - Fenix 7 Series

Ranked #1
Garmin - Fenix 7 Series

Ranked #1
Garmin - Forerunner 255 Series

Ranked #1
Oura - Oura Ring Series