I used the Frequency Analysis function in EAC (Exact Audio Copy) to discover which was the best format for compressing audio. Obviously having it uncompressed is the ideal option but it is not always possible to do this on computers (generally due to memory problems), so ehre is what I found.

I used Wanted Dead Or Alive ripped from the This Left Feels Right CD layer of my SACD copy of the album.

This is the frequency analysis for the original WAV file:



This is uncompressed so contains the full set of frequencies for the song.

MP2 128kbps:



This is quite heavily compressed, and 128kbps seems to be a standard that people use, but as you can see most of the frequencies above about 15khz have been cut.

MP3 128kbps:



Again I have used 128kbps and again it has cut frequencies this time moreso, cutting at around 14khz.

MP4 128kbps:



This is the new standard of music soon to replace MP3 (probably), and is not quite as compressed, only cutting at around 17khz, but this is still a lot.

OGG 128kbps:



It seems OGG is the best of the compressers I have found, as it only cuts at around 21khz, keeping most of the frequencies and thus losing little. This probably makes it the best of all the formats to use, and also it allows higher encoding rates than MP2, MP3 and MP4, allowing up to 512kbps whereas the others stop at about 321kbps

WMA 128kbps:



This is the standard for Windows, and is less lossy than MP2, MP3 and MP4, only cutting at about 18khz, but this is not as good as OGG.

It seems if lossless formats are unavailable due to memory restrictions, then OGG is the best format to use.