I had the Charge HR and upgraded to the Apple Watch.
For pure fitness tracking;
1. Fitbit gives you better feedback on activities. (graphs, time in HR zone, etc)
2. The AW emphasizes a better quality day. (instead of merely counting steps like Fitbit, you are concerned with time in HR zone as well as movement > the three rings of the AW).
other bits;
Battery on my Charge HR lasted 4-5 days. AW - 1.5.
AW notifications and apps - obvious item but I enjoy text messages, etc on the wrist, stop watch, turn by turn nav, etc
The AW is cool and I do enjoy it more than the Fitbit. However, given a do over, I don't know that I would purchase it again (or Fitbit or any other wearable for that matter). This is all early tech and I'm not feeling this "always connected" direction of things and having yet another screen or thing to charge. From a fitness perspective, they are "OK" and probably benefit some people who need a reminder, but for serious fitness, stick with a HR monitor and an app on your phone. Plus, half the people I know who wear Fitbits don't even exercise.