Compared Roku vs Google TV vs Amazon Fire Stick for my Tablo device. I connected via ethernet to get best picture and limit wifi lags. Happy to say that the picture quality of the Roku is better than the others. It is crisp and the menu loads quickly as you scroll through the channel guide.
The Amazon menu/home page is annoying and full of ads and clutter. Also, it was proned to lags and freezing due to all of the content being pushed.
The Google TV was adequate but picture quality was unacceptable - fuzzy in some occassions and generally dark.
The Roku stands out except for one area - menu and navigation choices. Very dissaponted that the Roku menu lacks convenience offered by the other devices such a "return to live tv" button and the ability to see the channel listing and guide while in live TV. Feels like Roku just offered stripped down Tablo app.
In th end its down to Google picture issues vs Roku's lack of navigation ease. If I can fix the picture issues, it's Google all the way - unless Roku gets its act togeher and impoves the app.