I find myself unable to specify a most beautiful chord in isolation. It's the same as trying to find the most beautiful rhythm. It isn't a meaningful question for me personally, even in a comparative sense, if only for the reason that any musical element hardly ever occurs in isolation. There are certainly chords, rhythms, melodies, textures and so on which I consider very beautiful in their context, but if I play them in isolation they do not seem so remarkable.
Even worse than this, and more generally, within a very large acceptable variation I have great difficulty in picking out the most beautiful object within any given class of objects. It's just the way I'm made, I think, because many of my friends perform this latter task at once and with absolute sureness. They can look at a hundred photos of women, birds, landscapes, clothes, for instance, and single out one in a matter of seconds as being the most beautiful.