What is the best format for compressing PS1 isos?

I have a collection of PS1 isos and I want to save storage space and have the file ready when I want to play. Emulators do not read .rar, .zip nor .7z and it takes some time to uncompress the files. I do not want to decompress the file whenever I want to play an iso. The use of .ecm does not discard the use of other compressors.
The .cdz format is read only by psxfin, which is abandoned and unfinished.
Some emulators read PSP's .pbp, but I am not sure if I can convert it back to .cue/.bin, because I want to have the clean unmodified iso and I do not want to use irreversible compression.

Any help will be appreciated.
Thanks.