7-zip is as far as iknow the best compressing algorithm out there. But it has a big dissadvatage. Compression speed! I have an old release (4.44) so maybe the latest rel. (4.57) have better speed. It is the best and here's why:
My first and only test was when some time before years someone released the bioses from gamecube for all regions, decrypted and encrypted.
I used the latest (for then) winrar, winzip and 7zip.
At all programs i used the best options (winrar: compact,best# winzip: maximum(deflate), 7zip: lzma (reasonable method, because ppmd is sytem sources eater
), dictionary size 128mb, word size 273 which these settings made use of 1375mb of ram :$ so only for those who have more than 1gb ram and 512mb pagefile).
The results: Uncompressed: 21mb, winrar: 17mb, winzip 18.5, and 7zip 4mb!!!
So the best option (if you have the time to drink a big cup of coffe and let your pc do the job for some hours, otherwise there is the priority option at the taskmanager) is 7-zip!
Sorry if you bored reading this. I hope i cleared out some things about the best compression program.
pH0eN1x