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

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I went to Polar Pacer for 18 months after always being Garmin. It had to be sent for warranty repair 3 times and broke again when I finally gave up. Software issues were constant. I'll never buy another fitness watch that isn't Garmin again.
Sad but they are running out of time , basic up to date watch is the M3€400, THE Pacer Pro, Pacer, and the Ignite are all out of date( i have the Pacer). Coros, Amazfit, Huawei, Suunto caught up. Pity ,but never forget what happened to Nokia, Blackberry. I wish them all the luck in the world 🙂
I ended up ordering the Polar Pacer and H9 this week. I would get the Unite, but I was worried the crappy battery life would make me angry like the A360 did. I am a huge fan of Polar's heart sensor and the app, that's what I'm here for... I never purposely used GPS but I noticed my phone would somehow track my movement during a bike ride when the watch was tracking a workout and connected (for text notifications).
I was in the same situation as you and just started training again. I bought a polar pacer secondhand cheap as good as new and am very satisfied. I was considering the garmin forerunner 55 as an alternative but went for the polar pacer because to me it just looks better.
Get yourself a polar pacer
Yes, the Pacer is the newest of the three watches you mentioned and sounds like it would be a decent choice. Both the Ignite and the Vantage M series are now on version 3. You could use your H10 with any of these watches to get more accurate heart rate data. There is no official way of importing workouts done with a non-Polar device into Polar Flow. There are third party apps that can kind of do this, but the training load may not be calculated. The easiest way would be to record your bike rides on both your Garmin and your Polar device.
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

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Oura - Oura Ring Series