Speed definitely depends on use cases. I switched from Vim to Emacs because Vim's syntax highlighting in LaTeX files was so slow it lagged behind my typing (and I am not a fast typist!). This is a well-known problem in Vim and the manual even has a section about it (see :help tex-slow). Emacs was perfectly snappy for LaTeX and I didn't want to use one editor for LaTeX and another for everything else, so I just switched to Emacs for everything.