Well, the easiest IMHO is the Android TV box (mainly because it comes with a remote) but I personally have a cheap Mini-PC because I used it to do a lot more than just being a media box and it still just sits in the living room in the TV stand.
Way back when I started (trying to have something in my living room, rather that absolute started which was way before that) all that I had was a cheap media box with an interface that was basically a file browser, accessing files over Samba.
Stuff is way fancier nowadays AND you can do it with much cheaper hardware if you want to.