We've been through a number of streaming devices in this house, including obscure stuff built into TVs and crappy set top boxes. Roku is the best. It's independent, so all the apps work great and nobody gets special treatment. The software is excellent and easy for all the kids to operate, unlike many other devices that claim to be "simple".
The thoughtfully designed remote doesn't require line of sight since it doesn't use infrared. This is a big deal in our house. Plus it talks to our TV so we can use it for power and volume.
Plus it's cheap, at least IMO!
Addendum: The Roku comes with a nice Apple TV app so we can watch all of our previously purchased Apple movies. Roku is completely agnostic when it comes to content.