Something I forgot to mention earlier: if you search for "the
greatest piece of music ever" on Google, the results are much
more dominated by Beethoven's Ninth and Handel's Messiah than if you search for the
best piece of music ever, which brings up more random pop and rock songs.
So is there a distinction between best and greatest? Some people make a clear distinction between what they consider greatest and what they enjoy the most. Guilty pleasures are not great though they may be very good. The pieces considered great tend to be very big ones, like the above or Wagner's Ring cycle. I suppose that makes etymological sense, at least.
(Listening to all of the Beethoven symphonies, one thing that strikes me is how different in length they are. The Ninth is
gigantic, even for a major symphonic work; it runs about an hour, and even the famous choral movement is longer than some of his earlier symphonies, at about half an hour if you include the five-minute instrumental prelude where the Ode to Joy theme comes in for the first time in the strings. I remember hearing a rumor that the 70-minute CD format was determined by the length of some recording of the Ninth that some executive liked. But the Fifth is actually kind of short and really clips along.)
Correction: I misremembered: the last movement is really only about 21 minutes long. That's still pretty long for a movement.
Also: Here's the
Snopes page on the CD length legend, which is probably bogus. For one thing, most modern recordings of the Ninth Symphony are, as I said, more like an hour.