What is generally considered the greatest clical piece of all time?

Well I have done quite a bit of studying on Beethoven and some on Mozart. The most famous might be Beethoven's 5th Symphony. I mean a lot of people may could tell you want symphony it is and who wrote it by just the first four bars. Most other pieces people may need a hint, even if they know who wrote it they might not knows it's name, or vica versa. The greatest...well I don't know. Mozart Requiem was astonishing, although I guess he didn't write all of it. Beethoven's 9th was terrific. I would say Beethoven's 9th, the Ode to Joy(4th Movement). Some people know that one too just by a few bars I'd say, plus who wrote it. But you are not asking the most popular, but the greatest. Is there a difference... I like this question because it makes me think. Do you want to eliminate the Baroque period. Some might argue that Bach wrote the greatest piece. Did you know that he went blind? How much more then difficult for Beethoven who went deaf. Such geniuses. Chopin was no amateur either, although he was in the Romantic time. Some say that Beethoven lead to that time, or that he was the transition. I would say Beethoven's 9th...it was astonishing. Listening to it makes me think of a victory.