I think the best motion sensor is a video camera with motion sensing software.
Perhaps a bit ironic, but the reason I started with Smartthings was due to the unreliability of my video-based motion system. A video based system works by looking for pixel differences between frames. The software can be tweaked to require a certain number of pixels to change (in order to reject small objects), for them to change by a certain level, that they be contiguous, there can be some attempts to prevent light changes from triggering the system. But fundamentally it works on visible light so a cloud passing overhead was triggering my video system, and on the outdoor cameras a tree in the area I wanted to monitor blowing in a breeze would often cause a trigger. Also my cameras had an IR light that automatically came on when the light level fell too low; every evening as the rooms became dark this would cause the software to trigger an alert (perhaps if the scene detection is in the camera itself it can briefly suppress detection when the IR light turns on or off).
A motion sensor, by contrast, works on infrared light. It looks for changes in the infrared signature of what it is seeing. This renders it more immune to passing clouds or blowing trees.
The video system would probably work pretty good in an interior room.
BTW I also bought a pair of the Aeon sensors for my yard and they are completely unreliable. I am waiting to hear how the Everspring ones work.