I use an Apple Watch and a Fitbit Blaze.
If you want really good notifications and an ok fitness tracker, Apple Watch.
If you want a really good fitness device and ok notifications, fitbit.
Comparison:
Steps: Apple watch is much more accurate and doesn't count as many steps when driving or on a bus
HR: Apple watch takes a reading every 2-16 mins. Fitbit Blaze every 5 seconds. HR is accurate on the Fitbit
Auto activity recognition: Fitbit detects cycling, walking, running, etc over 10 mins automatically. Apple watch doesn't
Stairs: Fitbit only
App: Fitbit app is better, showing resting HR, and a graph, steps, stairs, auto activity. Apple Watch activity app is too basic. Even when going for a run it doesn't show much.
Notifications: Both are good. Apple Watch has a better vibrate.
Battery: 5 days for Fitbit, 2 max for Apple watch
Sports bands: From CEX about 5-£8 - AW £12+
Hope that helps!