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

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I have an ultra 1 but it doesn’t have a dedicated triathlon so I went with a Garmin 965
Bought FR965 on sale for 450 2 weeks ago
Bro you can get a "used" (often actually still new in box) 955 on marketplace for like $300. The only complaint I have about mine is the barometer/elevation data is jacked up, but that doesn't seems to randomly occur with different garmin devices and isn't isolated to this one. The 965 is basically the 955 with OLED, which isn't a real upgrade to me. The 970 is marginally more advanced. But don't spend $500 on it, that would be crazy for a watch 2 generations behind.
Forerunner 55 for the absolute basics. Forerunner 165 is the cheapest with a AMOLED screen. Forerunner 255, 265, 955 and 965 are just discontinued. In my opinion 955 is the most value for money as it includes mapping. 965 is the same watch as the 955, but with an AMOLED screen. If you don’t need mapping, then go for the 265. It is the same as the 965, but without maps. So if you can find a 955 that would be your best bet in my opinion. Forerunner 570 and 970 introduce unnecessary features, such as microphone & speaker, sapphire glass, shiny metal bezels all of which add nothing to running but do increase the price.
I have a 965 and I charge it for like an hour a week whether it needs it or not.
Venu 2 plus and I currently use a FR965
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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Garmin - Fenix 7 Series

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Garmin - Fenix 7 Series

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Garmin - Forerunner 255 Series

Ranked #1
Oura - Oura Ring Series