I’ve tried Tablo on Chromecast, Fire TV stick and both generations of the Fire TV. By far the best were the 2 Fire TV boxes, especially the newer 2nd gen version. Things just run super fast on there, and syncing typically only takes seconds - where on other devices it can take much longer. If i had to recommend one to someone I’d say the newest Fire TV box. I also use it for PlayStation Vue, which also runs great on Fire TV.
Is there anything that Fire TV won’t do that Roku will?
Fire TV doesn’t do VUDU, Google Play Movies, or 4K YouTube (that I know of).