This is of course the age old debate, which on other sites has been known to quickly devolve (one of the Internet ‘holy wars’ of yore). Nonetheless, I am curious.
I personally use vim. Part of the reason is surely that it is just the first one of the two that I happened to use, and thus by the time I tried emacs I was used to vim. But more broadly, I enjoy using vim because once you get over the hump of ‘weird’ commands and modes, I feel that vim most closely emulates the feelings and thought process that you have when building something with your hands. You can pick up different tools, yank pieces out and rearrange them, turn the object around in your hands to see different parts, etc etc. Once you internalize the movement and editing you really start flying around. At that point the interface seems less like a barrier between you and the text and more like a way to ‘hold’ it.
Of course, people have different preferences.