I had a second generation (or it might have been third) Apple tv for about a year in use, finally sold it several months ago after not using it for near on a year. I'm completely non techie and know nothing about the guts of this stuff. I can say that it was a decent device and is very helpful if you already have a ton of other Apple devices, I had just gotten my iPad at the time we bought it. It did tend to need to be set back to factory and rebooted fairly often, sometimes two and three or more times a month, other times it would be fine for several months. I never used anything but Netflix, iTunes and YouTube with it and used the Airplay feature to stream stuff from my iPad to the tv with it a fair amount.
However, my husband is decidedly not an Apple fan and doesn't own any other Apple devices, which leads to one of my big complaints about Apple, their various stuff meshes-syncs, wonderfully for the most part but Apple stuff generally doesn't play well with others! Once I married him and was the only one with the Apple devices that didn't get along with his various other gadgets, the Apple tv got put into storage because his non Apple gadgets all worked together but not with it.
If you have limited other Apple devices you want to be able to stream through it, the Roku is every bit as wonderful and considerably cheaper. We personally use a PS3 for our streaming but I just bought my Grandparents two Roku boxes a few months ago and have been very pleased with them. I have also heard wonderful things from a few of my relatives about Chromecast.
I never really went looking deeply for content on the Apple tv, so I could be wrong, but I was very impressed with the available content on the Roku, it seemed to have a lot more than the Apple tv did.