The best replacement for flac is mp3.

The best alternatives to flac are rated as following:
★★★★★  mp3
★★★★  wav
★★★  alac
★★★  apple lossless
★★  aac
★★  ogg
★★  aiff
★★  ape
★  320
★  wma
★  wma lossless
★  m4a
★  cd
★  vinyl
  320kbps
  mp3 test
  320 kbps
  wave
  mp3 320
  v0
  ogg vorbis
  wav file size
  shn
  flac hd
  lossless
  monkey audio
  dsd
  320 mp3
  mp3 difference
  mp3 quality
  320 kbps mp3
  wav better
  mp3 size
  aac better
  320kbps mp3
  wavpack

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

Other search terms related to flac and their ratings are:
★★★★★ eac
★★★ winamp
★ cue file
★ album art
You have in mind a companion for flac and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of flac in all years. Click on graph for more.
flac
mp3
wav