It depends. If I'm watching a movie, I obviously want the highest quality, and it really annoys me when the app doesn't have a feature to force the quality. Great, that means the movie is canceled and I'll have to try again at some arbitrary later time, because I'm not going to watch it as a blocky mess just because their servers are having a moment.

If I'm watching a live stream, I'll take whatever quality currently works. Waiting to buffer it would mean I'm behind everyone else...