I would still say CHD is the superior compressed format, since it's fully open source (PBP is reverse engineered from Sony's proprietary format) and the tool to compress to it comes from MAME's official site. I would upload PSX2PSP to VirusTotal before running it no matter where you get it from. CHD should have better compression for redbook audio games too, since it compresses it with FLAC. CHD's only real weakness is no support for multidisc games in a single file, but is it really that big a deal to create .m3u files for those? It's just a text file with a list of each disc's filename.