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

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I second the Garmin if you have iPhone, but can be pricey. If Samsung, the Ultra. The 2024 model is a deal, but they all work well. I'm currently using the Ultra 24, GW8 and GW8 Classic.
If you have tattoos where a watch would sit then I'd avoid Samsung. I used to have an apple watch ultra 2 and the sensors on that were great over my tattoos. I changed to android and got a Galaxy watch 8 classic and it wouldn't detect anything at all. I've now got a pixel watch 3 and it works great.
I've had a 6 classic for a few months (with my new Fold 6) after using iOS and apple watches since the first apple watch was released. I've been disappointed with the 6WC's sluggish performance and unresponsiveness compared to the apple watch so I've already ordered my 8WC. Plus I love retro watches and the 8WC looks like an old divers watch 😊 What would have been even cooler is if the bezel was red/blue split like the 'Pepsi' styled watches. But black will do just fine.
The Ultra has about the same amount of battery as the 5 pro (I went from the 5 pro to the Ultra last year). The 8 classic has a smaller battery, so it won't last as long as the 5 pro or Ultra. The differences between the 8 classic and Ultra are... - The 8 classic is made of stainless steel, the Ultra is made of titanium like the 5 pro - The 8 classic has a smaller screen at 1.34 inches. The Ultra has a 1.5 inch display (the 5 pro has a 1.4 for comparison. You most likely won't notice the difference in size between the 8 classic and 5 pro but the ultras screen size lools noticeably bigger). - The 8 classic has the fan favorite rotating bezel where as the Ultra is like the 5 pro and only has the digital one. - The 8 classic has a 445 mAh battery, whereas the Ultra has a 590 mAh battery (same size as the 5 pro) Apart from those things, the 8 classic and the ultra have the same specs. Same possessor, same GPS, same health sensor and same amout of storage at 64gb (if you get the 2025 ultra, the 2024 ultra has half the amout at 32gb which is double what your 5 pro has at 16gb). My recommendation is that if you want a watch that feels like an all-around upgrade of the 5 pro I would get the Ultra. If you want a watch with a similar battery life to your 5 pro, you won't get that with the 8 classic. I would recommend going into a store and checking both of them out first because they are both very different styles to the 5 pro. Personally I like the look of both of them (but prefer the Ultra, but I might be a bit biased, lol). The Ultra is ever so slightly bigger than the 5 pro because of its shape but you honestly shouldn't notice a massive difference if youa re ok with the 5 pro. As I said above, definitely go check both of them out before pulling the trigger on one but my recommendation is the Ultra.
If you’re looking for WearOS watches (since this is the Android Wear subreddit), there aren’t many options: Samsung Galaxy Watch (the only ones with ECG), Pixel Watch, and OnePlus Watch. There’s also Mobvoi and Xiaomi, but their last model came out two years ago, so it seems like they’ve given up. I have the latest Galaxy Watch8 Classic, and it looks good. It offers a 24-hour battery life with all features turned on, just like a phone. There’s also an LTE version, so you can leave your phone behind from time to time.
2 days on average Source: I have it
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.

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Oura - Oura Ring Series

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Apple - Ultra Series

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Garmin - Fenix 7 Series

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Garmin - Fenix 7 Series

Ranked #1
Garmin - Forerunner 255 Series

Ranked #1
Oura - Oura Ring Series