I have a 2015 Shield TV and a Mi Box S (got it on sale at Walmart for $30). For just streaming video, the Mi Box S performs very well and opening apps is just slightly slower than the Shield TV. I have the Shield in the Theater Room and the Mi Box S in the living room (both hard wired -- adapter for the Mi Box S) and both can direct play/stream a full Blu-ray rip through Plex with no issues.
As for the others they are only alternatives if and only if you don't mind another OS and UI. Otherwise the Mi Box S is the best alternative for pure Android TV (and the perks that come with it)
I hate admitting this because the UI is dogshit, but the firestick is far superior to the MiBox. It just works better. I've a hanful of mibox's since they were released and am slowly changing them out for firestick. Mostly because they can handle HDHomerun streams and mibox can't unless using ethernet.
You want something that will be fully supported and not have issues with playback, get a shield or a 4k firestick and slap hijacklauncher on it with your launcher you like, done deal.