I've been a Netflix subscriber for 6 years and had a Roku for over 3 years. Pre-ordered it directly from Roku and was one of the first 5,000 customers in the US to get it. Now I have 2.
Streaming Netflix is great. The list of movies/shows is getting longer all the time.
Streaming quality of Amazon Prime Video is lousy, practically unwatchable. Don't bother paying the $80/year if you mostly want the video service.
The other channels are nice, but to be honest, nothing else on there that's free is the equivalent of a cable channel.
I haven't had premium channels on my cable in almost 20 years.