In my experience the filesize difference between lossless MO3, IT2.14, and J2B compression is insignificant. IT2.14 is supported by the most players, MO3 is the easiest to accurately convert to (and almost always the smallest but not by much), and J2B is the only one supported by unmodified JJ2. If I recall correctly J2B compression is lossless, whatever Treylina heard was probably something that screwed up while converting it, rather than lossy sample compression.

ahem. mentos.s3m