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

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I’m pretty sure the Instinct 2 and 3 both use the same sensors and, internally, are quite similar. I bought a base model 45mm Instinct 2 at the tail end of 2024 to replace my AW6. Great move. I’ve been trying many Garmin MIP watches since but keep switching between the Instinct 2 and a Quatix 7 I snagged on sale. The base Instinct 2 is a great and affordable introduction to Garmin. It often goes on sale for under $300CDN and is easily available at big box store, so you could try one new and return it if it isn’t your thing. (I’d bet you will keep it.) The updated look (orange) and flashlight are the biggest changes with the 3, as far as I recall.. And OLED, if that’s of interest to you. Getting away from an OLED screen was one of the draws to the Instinct line for me.
What features do you care about most. You mentioned two of the most full featured watches but to recommend the most bang for your buck you need to know what your must have features are. As for future updates, don't buy technology based on future updates. Buy based on today and anything that happens in the future is a bonus. It's too hard to predict how companies will treat updating even their most cutting edge devices
You're in luck. The Instinct 2 can do both of those things and since it's no longer in production you can find some deals on it. It's under $250 on Amazon right now: https://www.amazon.com/Garmin-Instinct-Multi-GNSS-Tracback-Graphite/dp/B09NMMN9W8?th=1
I would agree with the other post, if you want to get into tris, garmin is your best bet. The cool thing is, while the top of the line models are expensive, a couple of generations older are still awesome. My recommendation would be for a Fenix 7. Running about $450 on amazon new. [https://amzn.to/49DghWh](https://amzn.to/49DghWh) If that is a bit too pricy, you might try the Instinct 2 or 3. I have (and use) an instinct 2, that is very rugged and currently only $215 on amazon: [https://amzn.to/489fVUD](https://amzn.to/489fVUD)
Garmin Instinct 2 non-solar is the exact watch I currently have, and it does everything I need. Currently It’s on sale for $169 until they go out because they released the instinct 3. Does everything triathlete could want and has a bunch of extras like (limited) GPS navigation for hiking, weird sport profiles like kayaking and rowing, 28 days of battery life (about 14 days with my 6 workouts a week), etc. About to use it for a triathlon then starting to train for an ultramarathon with it. Wonderful watch that I will use until it breaks. https://www.garmin.com/en-US/p/775421/
My priorities were battery life, form factor, and price. I chose Instinct 2 non-solar because the battery life lasts close to a month between charges with light use (regular GPS use will drain it faster but still not fast enough for me to care about solar) so I didn't need the extra cost. It's great for everyday use, super rugged, and I like that I have sleep tracking data basically every single day because I don't have to charge it overnight
The instinct 2 solar has a solar panel over the main part of the display, which makes the display much less readable. If I were going to save money, I would get instinct 2 without solar which has much easier to read display. If you want solar, I get the instinct 3 whose solar panel is only on the outer ring. Was $300 for a few weeks Nov/Dec in USA. Not sure if it could be had for that much at the moment.
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

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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