The best replacement for muff is fumble.

The best alternatives to muff are rated as following:
★★★★★  fumble
★★★★★  fuzz
★★★★  fuzz face
★★★★  swollen pickle
★★★★  tube screamer
★★★  rat
★★  tone wicker
★  metal zone
★  fuzz factory
★  boss ds 1
★  fullbore metal
★  proco rat
★  ds 1
★  tl-2
★  ear plug
★  tone bender
★  fullbore
★  ds1
★  boss ds-1
  mxr fullbore
  metal core
  micro metal muff

Your alternative for muff is not listed? Suggest!
Speaking about muff, one probably shouldn't forget about tube screamer.

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



Google Trends

Scale is based on the average worldwide traffic of muff in all years. Click on graph for more.
muff
fumble
fuzz