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

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almost my case. I still have garmin fr945, suunto 9 and vertical 1. both suunto have big troubles with hr measurement, sleep accuracy not good. for cycling I have wahoo bolt v2 and v3, for concept2 - only ErgData app. withings smart scales is more than enough for me. one thing for me what suunto is missing is “resume later” function, especially for walking or hiking. I like suunto maps and navigation. now I’m confused to choose vertical 2 or race 2. both have better (I hope so) hr measurement and… thats all. ok ok, vertical 2 have led flashlight. vertical 2 disappointed me without local music storage and without nfc. but I like suunto for menu design, because garmin UI looks like designed for childs - not solid.
As an owner of 9 Peak, Vertical 1 and Race 2, buy Garmin without hesitation.
I came from Apple Watch, briefly to Garmin, then got a Vertical (1 - steel solar) a year ago. I too thought it was a great looking watch which is why I bought it. I cant speak for everyone here bc the Suunto reddit group seems to be a place where people bitch about Suunto, so ALL YOUARE READING HERE IS COMPLAINTS. I am here to tell you that the experience with the app and the watch is great and it is a better looking watch than anything the competition has and... isn't that part of the point of a watch? Though admittedly I am not an elite athlete or anything but I do bike/hike/run a distance of 50-80 miles per week (according to watch) with the occasional loooong bike ride and it seems just fine for me. Software and sensors seem just as good as the Garmin I had. I way prefer the Suunto APP to the Garmin app and drawing bike routes on it is great and better than strava, which I still use for some reason.
Edit: original comment I replied to just said "Because the battery dies after a day". Maybe for an Apple watch? Really inaccurate for any modern watch designed for the activity. My Apex 2 Pro lasts for about 3 days straight tracking my location, and I don't need to track when I'm stopped or sleeping. It realistically gets me 5 days of use between charges. If I ever do more than that, it's battery is so small it barely affects my power bank. Or if you regularly do more, the Vertix gets double the battery life. Garmin or Suunto have similar options and capabilities too.
Not only 1 right answer. Coros, suunto, polar are all great watches and honestly it comes down to user. I have suunto vertical which have medicore WHR, their 2nd version of vertical 2 and race 2 improved that. But coros vertix, apex 4 or pacer pro are also great options. Consider some models from polar aswel, like grit x2 pro, vantage v3, etc. Garmin have lots of options aswel with their forerunner and fenix and enduro series. My suggestion would be to check out dcrainmaker reviews and some yt reviews to see what watch can offer you. Then download their software and play on your phone to see how good/bad software fells for you. I am unaware what ios integration will be since i am an android user soo yea. And yea at the end its realy user based as long as you go with watch with dual band gps systemy onboard maps, and other stuff. Garmin is leading in maps since only on their watches you can reroute your route on watch itself, other brands requirw phone to do that + garmin have the most smarr functions. Soo yea also i am suunto user soo i would say suunto but some1 else might dislike suunto soo again not only 1 answer but many options. Garmin is the best but some dislike their app which is harder to use than some others plus price. Suunto is behind in smart functions + can be buggy (mine is flawless but many have problems with newer watches), coros i ve heard lots of complains witz their sensors for alltitude and gps but that might be just users who dont know how to use watch properly, etc. Soo yea read some reviews 1st.
Suunto has different battery modes for activities. For multi-day events, you can select different modes that use less features to extend the battery. EG, for the Suunto Vertical: https://us.suunto.com/pages/how-do-i-get-the-most-out-of-suunto-verticals-battery-modes
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