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

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Although it's much smaller, I prefer my venu 3s over my galaxy watch 7, will probably upgrade to the venu 3 sooner or later, but for now this is perfect
I am using Galaxy Watch 7 and Amazfit Active 3. Amazfit is closer to my professional medical devices from work. Edit: and topo maps are better than any app on Wear Os
From an older Galaxy Watch? Yeah the Pixel Watch will be more accurate. From a Galaxy Watch 7 or 8? It will be roughly the same. GPS was an area of difference but the GW7 has been improved with updates and the GW8 is pretty much par with PW. For most cases any of the major smart watches like the GW, PW or even AW are close. So I wouldn't make your decision on that basis. Comparing the Galaxy Watch and Pixel Watch I'd look at what device you're pairing it with and the unique features each offers.
Worked fine on my GW7. Guy who made it put out a video walk through recently with the latest way to do this. https://youtu.be/xSjURFKQB2A?si=ZrinWNT3nhN3yLDG
I've been eaten alive for saying this, but I'll say it again. Most information available comparing smart watch accuracy find them pretty close to each other. If you want something to generally track this information then Galaxy Watch is a perfectly fine pick. If you're doing more extreme sports then someone more rugged like a Garmin smart watch might be a better pick. If you want the absolute most accurate measurements then get a medical device that measures that. Smart watches are not designed or claim to medical devices. Just accurate enough to be useful overall. You may have times where it misses something or has blips but the overall result is accurate to be actionable. And Galaxy AI can offer suggestions that may be helpful in improving your health or exercise routine.
I just upgraded to the galaxy watch 7 (just set it up it minutes ago) 40mm and the Watch 4 classic looks better and the rotating bezel protects the screen. I'm a little scared to break or scratch the glass of the 7. But it's quicker indeed, and lighter but let's see if battery life is better, I don't use the screen always on but was having bad battery life on my aged watch 4, that wad the main reason. I considered the OnePlus Watch 3 for its great battery life but since I own a Samsung s24 ultra decided to buy a used 7 for 81 euros.
If you're worried about battery life, I wouldn't go lte. Drains battery faster. Same thing with your phone on mobile data vs wifi. My gw7 dropped almost 30% battery to youtube music in around 3 hours of playback. That was using my galaxy buds, and having the songs pre-downloaded... on the 44mm Bluetooth model.
Oh yeah without youtube, I took this thing off at 3 am yesterday... at 65%. Music dropped it to that in a few hours though.
I got a refurb from Amazon for 150 US, and saw it for 140 a week later. Looks and works like new FWIW.
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