FireSticks are inherently easier to tinker with. But Amazon bends you over with shoving ads and spyware up your ass at every opportunity. It is baked into the UI design itself. It is very advertising-forward, with everything else designed around ads. And even the 4K max lags at times.
AppleTV really requires an iPhone to set up optimally. And it is locked down with no clear jail break at this time for most people unless you’re willing to solder (or if I’ve missed a new flaw in an update which opened the door programmatically). But Apple TV is fast and smooth, with no inherent ads of its own. It is honestly over powered for its purpose, probably because it can also play a fair number of iOS games.
Chrome Cast with Google TV is a fucking mess. It is severely under powered to the point of lagging. It has half baked ideas like profiles which don’t change anything. And it has ads as the focus of the design just like FireStick.
But you’re going to pay a subscription if you go with Apple TV and want something like Infuse. Jellyfin and Plex, of course, don’t require it.
And despite what people say, Stremio is absolute dogshit on a FireStick because of its mobile-centric UI.
If you plan to use a server like Plex and Jellyfin, all of them work—but Apple TV works best. If you need anything else out of it, probably the fire stick if you use a pihole to stop it from phoning home for more ads constantly.