I started wearing a fitbit before the Apple Watch came out, and ever after I got the Apple Watch, I still wear my fitbit. It's one of the basic trackers that doesn't even have a screen so it's more like a bracelet than a watch. It's still a bit mystifying how each tracks steps/distance to me, as the Watch seems to count fewer steps but greater distance. Maybe when they start to sync up more closely I'll toss the Fitbit.
In the meantime, i would really LOVE some kind of Apple Watch band that you could just stick a small Fitbit tracker in so I don't need to wear two things. But I've got a very long streak going on my Fitbit and can't just get rid of it now...