For a conversion program, check out Amadeus Pro at www.hairersoft.com. It's an awesome editor, batch processor and converter that I use almost every day.
If you have access to a multitrack editor, try this trick for conversion. Make sure that you have a full-quality .WAV copy of the file you are interested in comparing. On one track, put the original wave file. On each subsequent track, place each version of the converted files. In order to compare, all you need to do is play the original on top of one of the converted files with the polarity of one of the two tracks flipped.
What this does is take two supposedly-identical files and play them in opposite polarity. Of course, the converted file has some data missing, so any material present in the original wave that the conversion deleted will play through. In essence, you're hearing a sonic representation of all the material that the conversion process deleted. With this setup, you just need to do a comparison of each conversion type to the original then pick whichever one has the least "missing" audio playing.