Samsung

The best smartwatch for fitness and health depends on your phone and priorities, but if you want the strongest overall choices right now:

• Best overall for iPhone users: Apple Watch Ultra 4 — Apple says it has its new Health Sensing System, stronger heart-rate sensing, and a readiness feature for daily recovery guidance. It’s the most polished health/fitness smartwatch if you’re in the Apple ecosystem. (apple.com)
• Best overall for Android users / long battery / serious training: Garmin Forerunner 970 or Fenix-class Garmin — Garmin emphasizes deep training metrics, robust workout tracking, and much longer battery life than typical smartwatches. (garmin.com)
• Best health-focused Android alternative: Samsung Galaxy Watch Ultra2 / Watch9 — Samsung highlights expanded health monitoring, sleep/recovery insights, and improved display/battery for 24/7 wear. (news.samsung.com)

Quick recommendation:

• If you use iPhone: get Apple Watch Ultra 4. (apple.com)
• If you use Android and care most about fitness training + battery: get Garmin Forerunner 970/965-class Garmin. (garmin.com)
• If you want a balanced Android smartwatch with strong health features: get Galaxy Watch Ultra2 or Watch9. (news.samsung.com)

If you want, I can narrow it down to one best pick based on:

1. iPhone or Android,
2. your budget, and
3. whether you care more about fitness accuracy, sleep/health, or battery life.