Short answer — top picks by use case (U.S., Sept 2025):

• Best for iPhone / all-around fitness: Apple Watch Ultra 3 — best activity + safety features for iPhone users (great GPS, advanced workout features, improved battery for long workouts). Pros: deep iPhone/Fitness app integration, multisport modes, emergency/satellite features. Cons: expensive, works best with iPhone. (theverge.com)

• Best for serious runners / triathletes: Garmin Forerunner 970 — industry‑leading training metrics, multi‑band GNSS and long GPS recording, excellent recovery/VO2 and bike/tri features. Pros: extremely detailed training data and long battery in GPS modes. Cons: pricier, less “smartwatch” app ecosystem than Apple/Samsung. (www8.garmin.com, tomsguide.com)

• Best for ultrarunners / multi‑day adventures (battery): Garmin Instinct 3 / Enduro-style Garmin models — rugged, solar/huge battery options and long GPS endurance for multi‑day outings. Pros: best battery and outdoor features. Cons: bulkier, less polished smartwatch UX. (techradar.com, tomsguide.com)

• Best Android (Wear OS) / balanced fitness + smartwatch: Google Pixel Watch 3 (or Pixel Watch 4 where available) or Samsung Galaxy Watch 7/Ultra — good sensors, solid workout tracking, and full smartwatch features on Android phones. Pick Galaxy for Samsung phone owners; Pixel Watch if you want Fitbit-style health integration on Wear OS. Cons: generally shorter battery than dedicated sport watches. (techradar.com, tomsguide.com)

• Best value / budget fitness watch: Amazfit Active 2 — strong set of fitness features (160+ sport modes, GPS), very low price and multi‑day battery. Pros: excellent value for casual users. Cons: fewer premium sensors and app integrations than Garmin/Apple. (techradar.com, theverge.com)

• Best for sleep & recovery metrics (non‑watch option): Fitbit Charge 6 or Oura Ring 4 — if you mainly want 24/7 health, HRV and sleep/recovery guidance, these give best passive monitoring. Cons: less on‑wrist display / smartwatch features. (mygizzmo.com, tomsguide.com)

Quick buying checklist (what matters most)

• Phone compatibility: Apple Watch basically requires iPhone; Wear OS / Samsung work best with Android. (Pick accordingly.) (theverge.com, techradar.com)
• GPS accuracy & sensor set: multi‑band GNSS, wrist HR + optional chest/foot sensors matter for serious training. (www8.garmin.com)
• Battery life: if you do long GPS sessions/ultras, prioritize Garmin/Enduro/Instinct class devices. (techradar.com, www8.garmin.com)
• Apps & coaching: Apple, Garmin, Fitbit and Google each offer different coaching/analysis — pick ecosystem you’ll use. (theverge.com, tomsguide.com)

If you want one simple recommendation:

• If you have an iPhone and want the easiest balance of fitness tracking + smartwatch features: Apple Watch Ultra 3 (or Series 11 if you want something less expensive). (theverge.com)
• If you’re a runner/triathlete or need the longest GPS battery and the deepest training metrics: Garmin Forerunner 970 (or Garmin Enduro/Instinct for maximum battery). (www8.garmin.com, techradar.com)

If you want, I can:

• pick the best single model for your exact needs (running vs gym vs casual tracking) and budget, or
• compare 2–3 models you’re choosing between (features, battery, price, pros/cons).