A:
I work in home theatre at best buy.
Roku stick: great for bedrooms in my opinion
Roku 1: used for TV's that do not have an HDMI input and it goes through RCA cables (yellow, white and red).
Roku 2: Slightly faster than Roku 1 and plugs in through HDMI
Roku 3: Faster downloading speeds than previous three models. (I have the roku 3) On the Roku 3 remote you have two features that are not available on the previous models. You have a headphone jack to listen to programs with headphones and it also has a search button that enables a microphone that can voice search (actors, movies, etc. over all the engines)
Roku 4: Same as 3 accept able to stream 4K content (like on youtube and netflix) and it has the same remote features as the Roku 3 but also has a feature to where the remote makes a noise so you can find it if you lose it.
All of the Roku products can screen mirror apple, android, windows, pc or mac. You can also download the Roku app on google play store or app store and use it as a remote. The app has other neat features as well.
Apple TV (old gen): Has nettlix, hulu, youtube, etc.
Apple TV (new gen): comes with actual gb storage on it. You can decide what apps you want compared to the previous model that would just give you a handful of apps (which I never used the ones they gave debut a couple).
Apple TVs are great if you have other apple products such as macbook, iPhone, iPad, etc. They can screen mirror images, videos, photos, etc. but you can sync your iTunes library to both models and wirelessly stream music and movies to your tv that are on your library.
I have both the apple tv (old gen) and roku 3. I enjoy them both but I have more customability with the roku. Haven't tried the new apple tv though. Keep in mind Apple products do not have amazon prime. The two companies have had issues and Amazon took all of their apps off Apple products but the Roku runs off of the google play store.