I haven't used any Apple stuff, but I've gone through many iterations of this over the past 15-ish years, going from MythTV to SageTV to Plex+Netflix, and using various iterations of Linux, Windows 7, 8, and 10 on everything from leftover PC part builds to the SageTV appliance to dedicated Mini-ITX HTPC systems to Raspberry Pis.
My main criteria is being able to use everything from the couch, using a single remote, and no keyboards. I was close to that with the SageTV boxes, but Google bought SageTV and it started becoming obsolete, and there was never really a good Netflix integration anyway.
I find the trouble with all PC-based stuff is switching between things and inconsistency between apps. Netflix on PC doesn't have a good way to do keyboard-based control, so remotes don't work well -- you pretty much need a mouse-style pointer. Plex works GREAT but the keyboard works differently than it does when you're using YouTube, and there's not a great way to switch. There's also all kinds of dumb problems getting multi-channel audio working with Netflix since they require some type of certified system or something.
A couple years ago I gave up on PCs and bought an Nvidia Shield, and it's basically the perfect device for me. AndroidTV is a great launcher, it supports everything I use (Plex, Netflix, Youtube, Weather, Baby cam monitor) and everything works with a single remote (I use a Logitech Harmony to control it + the TV + audio). No compatibility, rights or audio issues. And bonus: it is a Google Cast device, and also works with an OTA tuner (Silicondust HDHomerun -- though I never actually use that anymore). My TV never changes inputs: it's basically just a dumb display for the Shield, which now does 100% of content playback in my house.
It costs maybe a bit more than a nice MiniITX HTPC build, but just works (whereas an HTPC will take hours of time to get it working semi-properly).