After having used the board in all three views for some time now on different devices, my two cents on which I prefer to use.
Desktop -- definitely Indented, as it combines the best features of both the others.
Mobile -- Indented by a hair, especially if not on wi-fi.
Threaded: I love seeing the thread (seeing who is responding to whom), but I hate dealing with having to open up each post to read it. Potential slow speed when on 4G (comparatively speaking); small screen, my digits ...grrrr.
Indented: the indentation is so minimal on the small screen unless in landscape view, that it can still be difficult to tell which comment is being responded to by the poster. Might as well be flat. But in landscape view, the text of each post doesn't wrap as well as they do in the portrait view. Guess it's better than nothing. Minimal difference between the two renders the choice a coin flip for me.