I quite like RaspBMC (rather OSMC) nowI have been using Kodi since the very day of its inception, when it was XBMP (Not XBMC) (and no one had a clue as to what is was) and then actually converted the usage on a dedicated HTPC way back in 2011. (when I could afford one.. ) Shifted to openELEC and SSD in 2013.
Kodi for windows might not be stable,(hardly used that version) but have been using openELEC since 2013 and it has been nothing short of rock stable, yes initial releases were short on features, but as far as stability and boot timing goes, nothing could beat openELEC. Now I have it on 3 of my boxes (3rd now includes shield which has SPMC) and I am highly satisfied.
Not debating that Apple TV port might not be as good, but Apple ecosystem, just does not entice me
The limitations on the apple ecosystem bug me out honestly.. (ios specifically and now tvOS... OS X is a different beast altogether)
On the living room setup though where ease of use (for everyone) becomes important, tvOS is quite nice.. easy flipping between Kodi/Music streaming/Photos is quite appealing..
I switched to NUC when one fine day, power backup decided to fail when I was out of town post which the Rpi wouldn't boot into Kodi (until I came back and had to run a forced fsck)
The NUC still runs well but windows can be terribly flaky
Hopefully ATV 4 runs stable with no bug outs
On a side note, it do seem to be a good choice (so far) for a hassle free media box for new comers