TidBITS:

If you already have an Apple TV, I see no reason to rush out and buy a Fire TV, unless you want easier access to Amazon content. Of course, there’s nothing stopping you from having both a Fire TV and an Apple TV, if they’re within your budget and you have enough TV/receiver inputs.

In the end, I think the most important thing to realize about the Fire TV, and something that most reviews have missed, is that the Fire TV is merely Amazon’s opening salvo.

Good comparison between the two devices and, more importantly, services.