I've been using the Apple case for about three weeks and love it. Okay, it's a bit heavy and not exactly aesthetically pleasing but it means I can now sometimes go four days in between charging (I usually switch it to Power Save overnight and disable cellular - both through the control panel) and with the 30W USB-C Charger, it juices up both the case and phone at the same time - both hitting about 95% after only an hour.
I also love the tight iOS integration and there are no silly lights (that don't give granular measurements) on the back. The Apple case also completely covers the bottom and yet Apple's tolerances are so good that the speaker grilles line up absolutely perfectly. The black silicon also feels good with a nice firm grip. Apple's solution is simple and elegant. It manages everything for you, no on/off button or other such nonsense.
If you want a smart battery case, Apple's is by far the best option (IMO).