Roku offers a more platform-agnostic experience without relying on purchasing into a specified ecosystem to take full advantage of advanced functionality. The user experience lacks a certain refinement compared to the Apple TV, but it has a great variety of streaming apps available for users to enjoy their shows and movies.
There isn’t any overt gaming support available for the Roku that’s akin to Apple Arcade or Amazon Luna. This might not be a strong consideration for you if you already have standalone gaming devices.
They’re all certainly capable devices that support a wide degree of functionality. The core differences come from how they present the experience to the user.