Considered (and owned) several, including Samsung Gear Fit, Garmin VivoSmart, Fitbit Surge, Basis Peak, and the Band. I've stayed with the Band because it has the richest feature set, and performs reasonably well (sometimes very well) with all its features. Some of the others performed quite well in some areas, but not that good in others.
I also own (and still use) the Mio Fuse, which is the most responsive and accurate for HR, but is not as well rounded for 24/7 use as the Band, so I use it strictly for HR during exercise, paired with either Endomondo or IpBike apps. Quite honestly though, in most (but not all cases) the differences between the two in HR and calories burned are usually quite negligible. When it comes to calories burned, who knows anyway? There are wide variations in the algorythyms used in all these devices and apps. The main reason I stick with the Fuse is that with IpBike it allows me to use my speed/cadence cycling sensors (and power meter if I had one), and foot pod for walking/running. Microsoft's Health App still could use some work, but it beats the pants off Mio's own native app.
Basis Peak is quite good also, but very proprietary in that is doesn't really allow you to share or sync your data with any other apps. It also insists on sensing your workouts on its own, and starting/stopping them when it feels like it, and decides on its own what activity you're doing. Allows absolutely no input or editing from you at all.That and the fact that I eventually developed pretty bad skin irritation from its band forced me to give it up.
So anyway, for me, it isn't a case of any one most important feature that keeps me with the Band. Its that all the features work reasonably well, and (so far......knock wood) it hasn't caused any inflammation. Not to say I'm married to it, I'm evaluating a Garmin Fenix 3 right now, but the Band is pretty darned good, at least for me. Keep in mind that there is a huge variation in what works best for different individuals when it comes to these devices, since there are so many variables.