I'm a little biased with Fitbit. They are pioneers and made fitness trackers sexy again.
With apple watch one most annoying thing is that if you want to know the number of steps you have done, it requires 2 additional steps to dig into the step count. With fitbit and many other fitness trackers, it (step count) just stares at you on the main tracker window.
For me this is an absolutely must feature and apple watch fails big time doing this simple task.