I have been using the Amazon FireTV Stick for nearly 2 years now, bought it when I was in US during the launch.
Over time the interface has changed for the better with updates to the software.
I have never experienced any stuttering of video streaming over Wi-Fi for even upto 4K resolution videos from Netflix or Prime. I do not have the LAN attachment from amazon so solely dependent on Wi-Fi.
The audio quality from HDMI is stupendous, depending on the availability I have received Dolby 7.1 or stereo when on Prime Music.
Biggest advantage the ability to install additional apps like Spotify.
I have also installed Kodi on the fireTV Stick to access my home NAS so that I can enjoy my digital content.
Overall the appliance has not failed me in any department so far.