This paper from 2014 is a comparison of 5 different open source speech recognizers: http://suendermann.com/su/pdf/oasis2014.pdf

The Word Error Rates (lower is better) for each recognizer on two different corpora, VM1 and WSJ1:

  RECOGNIZER        VM1  WSJ1
  HDecode v3.4.1    22.9 19.8
  Julius v4.3       27.2 23.1
  pocketsphinx v0.8 23.9 21.4
  Sphinx-4          26.9 22.7
  Kaldi             12.7 6.5