I have Amazon Prime and I've been forced to pirate the content because their streaming app on the Roku 3 sucks ass. On the same device, the Netflix app never buffers (I have a 55 Mbps connection). So, I recently downloaded a series I was watching. Turns out, I had paid for it (Hannibal season 3), in HD. Just couldn't stream, over a few days, without stopped. So, torrenting I went.
I have the same complaint about HBO Now on the Roku. Man, does it suck.
Lest people think the problem is my network, often when I have the issue I switch to Netflix and never once have I had a problem after the switch. Seems unlikely I just happened to switch when the network problems went away.