I have the Fitbit One, which unfortunately has been discontinued, and a Series 2 Apple watch. I love both of them. I use my Apple watch a lot throughout the day and usually run the battery down, so I need to charge it daily. I do so at night, so I have never done any sleep tracking. As far as accuracy, it is great at monitoring walking, running and biking. Not so great at monitoring my heart rate for any workouts that have a lot of arm movements. There is a high intensity interval training mode that does a decent job of estimating heart rate and calories - might overestimate a bit. If I put it on the open goal mode it underestimates my heart rate and calories by quite a bit. I work at a school and have to mute my cell phone. The Apple watch lets me know when I get any calls or messages, which is great! It is also wonderful for setting reminders.