Similar to what cbsks said, Amazon Prime Video usually starts with low quality fuzzy video, which I've also seen happen in between while watching something. On Netflix, the video quality has been great from start to finish almost all the time. There have been only a few instances where I have seen fuzzy videos on it for a few seconds. This is over broadband that's usually at 40Mbps or so, which is way more than what these streaming services need for even 1080p quality videos.

On my Android TV, every Amazon videos starts at low quality before jumping to high res after a minute or so. This happens every time I start the app. Netflix never has that issue for me.

That minor annoyance is nothing compared to Netflix's auto-playing trailers, however. I actively avoid opening Netflix unless I already know what I am going to watch, and I close it immediately after I'm done watching it.