It depends on what you wanna do. I have an Apple TV because I have iDevices and it can mirror Movie Box (show box) and NFL and NBA games to my TV very easily and in high quality.
But I also have a cheap $40 media player called a Micca Speck for playing my downloaded files. The reason I went with that is because it plays ALL files, avi, mp4, wmv, flv, and most importantly for me mkv. It was the only one on the market I saw that could play anything you throw at it.
Between these 2 units, I have all the entertainment I need.