As far as performance goes, the Roku wins, but only because most of its channels have lightweight and crappy interfaces. The fireTV apps win for functionality but the fireTV stick doesn't perform well with these heavier interfaces.

I dislike the main catalog on the fireTV because it is cluttered with ads for Amazon streaming shows/movies, some of which I'd rather my kids not see. The main catalog on Roku is nice and clean.

I own both a Roku stick and a FireTV Box (returned the stick for the box) and we primarily use the FireTV because the interface is so much nicer and smoother (despite the stupid ads). We used have PSVue which is hands down better on FireTV than Roky. We have DirectTV Now which works well on FireTV but apparently the Roku channel isn't even supported on my version of the streaming stick which is lame.