This one is a win for Apple, which boasts more smart features than its fitness tracking companion.
An Apple Watch offers notifications, alarms, timers, Siri and a huge app store. By contrast, Fitbit has some basic services like notification mirroring, and a smaller app offering. You can use your Watch to make payments through Apple Pay, while only a handful of the Fitbit models allow payment via Fitbit Pay.
Apple Watch even has some models with Cellular capabilities, meaning you can accept calls and texts from your wrist, without your iPhone.
The companies also have slightly different approaches to music: with Apple, you can download albums on your watch from the likes of Apple Music and Spotify. On Fitbit, the only way you can download music is if you do so via Deezer or Pandora.
It's not a huge issue if you prefer to store music on your phone, but it does give Apple the edge in this category.