It really comes down to what content you want to consume and whether it’s supported on the Apple TV.
I bought an Apple TV 3 a few years ago and ended up selling it as I only used it for Netflix. The lack of support from TV companies, who had released apps on other platforms, was particularly disappointing.
Airplay never worked satisfactorily for me, but that might have been down to my network.
I’m in the UK so having free to air tv apps such as BBC iPlayer, ITV Hub, 4oD and Demand 5 was a key consideration. From what I can see, only BBC iPlayer is currently available for the Apple TV 4.
I think the Apple TV 4 is a more compelling device for US consumers than it is for those in the UK and that’s all down to the support.
I ended up purchasing a Fire TV, despite not being a Prime subscriber, as it natively supports the apps I want and allows me to sideload other apps, such as BT Sport.
Whichever device you decide to go with, I would primarily base your decision on what apps and content are available.