I've got apple tv and roku... I like both, but if I had to choose... I'd choose roku. To watch my vast collections of .Mp4 movies and shows, I have to load them in to iTunes for my apple tv to view them. Or... Just put them on an external drive for my roku to read them. And roku reads just about any file type.
The VLC app on AppleTV works well for file shares from Windows/OSX.
*Note to OP: You speak of a 4k TV. AppleTV only spits out 1080p.*
Here's some details from our setup:
I have AppleTVs for living room and bedroom along with a Fire stick in my workout room (only used for SportsCenter during workouts)
I use my parent's Xfinity subscription for authorizing all content. Not sure if you plan on using Sling for that but the app did just drop on AppleTV, been on Fire for a while.
I like the AppleTV interface better as it is a little cleaner but as I mentioned it doesn't do 4k.
I used to serve movies/music off my iMac (iTunes) but have migrated it all to a
Synology NAS which has apps for the AppleTV but not Fire.
The only thing I still run from a PC is
PlayOn, which I use to rip live TV streams from the
Xfinity site (and many more).
We do have an indoor antenna in the attic which I hooked up to the old cable splitter but we rarely watch broadcast TV, only if the network's app doesn't have a live stream.
As others have said, buy a really strong wireless router. We have a 100mb connection, unlimited data, $70/month but that wouldn't matter with a crappy router.
