[wrxtasy]

I can define my requirements this way:
   a) smooth perfomance
   b) RF/BT remote with voice control
   c) 4K/HDR/3D support, auto framerate switch
   d) Youtube/Twitch support
   e) fast gigabit ethernet (I don't have a solid wifi router, but in any case wifi connection is greatly limited in comparison with giga-ethernet)
   f) near-future flexibility which will allow me to simply change my 1080p projector to 4K HDR projector or TV, stereo to 5.1+

a & b) = Shield or Apple TV 4K, no 1080p 3D on those ever. Beware the problematic Shield BT remote, it's near universally despised, see THIS recent thread.
c) = Intel hardware, Zidoo X9S or RPi if you want 1080p 3D support with proper 24p support, no Voice control
d) = Kodi Addon or an App, and the Android TV Twitch App looks like rubbish, see HERE. A lot of people seem to use the alternate Twitchy App.
f) = 5.1 DD+ audio from Netflix, Amazon Apps etc on Android TV needs a DD+ HDMI connects audio receiver. The Apple TV 4K can downmix DD+ audio so has much better Dolby Digital only audio compatibility due to it's Dolby Audio licence, when using those Apps.

f) there is already a 4K HDR10 State of Play thread that has a lot of 4K HDR detail.

Pick what is most important and what types of ... Apps, audio, seamless SDR / HDR, 3D or Voice control you actually need.
There will not be a single platform that can do everything.