That ... - is what you don't really want to know by asking me. I won't put my foot in my mouth. The most beautiful work of music? No. Not here, not from me, not now.
As I made this experience myself, to search for the most beautiful piece of Bach's creations, I learned that you shouldn't leave such verdict to an other person. Because he or she firstly has his or her own taste. Which could be very different than yours. Secondly all collections with the motto "Best of Anyone" are always related to many commercial considerations too. Examples are, that it's cheaper to buy easy to perform pieces than very complicated works. One more is that with short pieces it's better to create a CD than with longer ones. Sometimes the reason just is, that you buy an already existing collection way cheaper, than if you put together your best selection. That is why I didn't like a "Best of Bach" CD, that is to say, I didn't really like many pieces. This actually was the reason, this website came into being, that is to say especially the "Bach Music Section".
Today you find a selection of the most popular and best known pieces on the page "Bach Work + Music", because in contrary to the most beautiful music pieces the most known and most popular compositions are clearly to research. On an objective basis, not on a subjective. However it's not a real scientific approach. But, you can get closer to what you actually want. Finally a little unscientific proof is as well, that I really love thirty of those thirty-three works much. There are only two, which I like less - and there is one only, which I "hate".
99 Music Calendars, Composers Calendars and Bach Calendars