The best replacement for mutter is compiz.

The best alternatives to mutter are rated as following:
★★★★★  compiz
★★★  murmur
★★★  kwin
★★★  muffin
★  mumble
★  metacity
★  midori
  grumble

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

Other search terms related to mutter and their ratings are:
★★★★★ xfce
You have in mind a companion for mutter and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of mutter in all years. Click on graph for more.
mutter
compiz
murmur