The best replacement for emacs is vi.

The best alternatives to emacs are rated as following:
★★★★★  vi
★★★★  vim
★★★  xemacs
★★★  eclipse
★★  sublime
★★  notepad++
★★  nano
★★  textmate
★  aquamacs
★  gedit
★  sublime text 2
★  sublime text 3
  vi editor
  gvim
  kate
  xcode
  counterclockwise
  geany
  vim python
  vi xkcd
  jedit
  vim xkcd
  bbedit

Your alternative for emacs is not listed? Suggest!
Speaking about emacs, one probably shouldn't forget about ess.

Other search terms related to emacs and their ratings are:
★★★★★ ess
★★★★★ gdb
★★★★ git
★★★ auctex
★★ scheme
★★ clojure
★★ x
★★ cscope
★ latex
★ lisp
★ ipython
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You have in mind a companion for emacs and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of emacs in all years. Click on graph for more.
emacs
vi
vim