Both suck as their software sucks.
- Limited options
- Closed nature
- Short support time (usually 2-4 year, even Apple has a bad track record for iOS devices)
- Not extendable/tweakable
A basic Windows box or MacMini, even 4 year old ones, blow Apple TV's and Smart TV's out of the water when it comes to possibilities and long term functionality. It may not look as nice and integrated, but I don't mind as the thing I watch usually runs 1-2 hours.
A TV has to do very little: play 24p/25p/48p/50i/p/60i/p over ONE input flawless judder free and with 1:1 pixel mapping and good color space support. Add a nice static contrast of 1:3000 or better, nice viewing angles, no backlight bleeding or uneven illumination, a nice wide gamut with decent sRGB limiting and we are done. Brightness to ambient light adaption might me another favourable feature, but that's it. And an awesome low standby wattage.
And it should not upmix, autocontrast, sharpen and color correct anything into 600Hz oversaturated halo-lined garbage. Just show the input, nothing more. It does not even need a remote! Ok, this is actually a monitor, but that is fine, a TV should be a monitor in 2013 IPTV land.
Problem is: try to check ANY tv on the above specs, or ask for these in the shop and they will give you the stupid face.