In my present experience, the best horn that I have had the opportunity to hear is the Aries Cerat Contendo 2. Its immense bass horn is expertly integrated with the large mid-range bass and mid-range horn, resulting in a seamless and commanding performance of great refinement and power. It is truly a wizard in its ability to perform magical acts before your very eyes. If it were within my means, I would acquire it immediately.
However, due to its size and cost, it remains out of my reach for the time being, or perhaps indefinitely. Other horns that I have also enjoyed include various Western Electric, Altecs, and Classic Audio Field Coils.