TeXmacs is vastly superior to LyX, but, more importantly, it is a completely different thing, with a completely different concept. The following is my opinion, which I cannot motivate in a detailed and well-funded way, based on experience of a few years of TeXmacs use and more of LaTeX/LyX: given the difference between the two programs (TeXmacs is not based upon TeX!) LyX does not have the potential to reach the quality of TeXmacs.