FreeArc seems like the most promising. Not only better compression than 7-Zip, WinRar, also faster! What they say.
From the FreeArc homepage:
"Compared to RAR and 7-zip, FreeArc at this moment lacks the following: multi-volume archives, 64-bit version, storing of file attributes/extended timestamps/NTFS streams in the archive, bcj2, data segmentation."
I could live without the 64-bit version and *maybe* the multi-volume archives, but the lack of storing file attributes and extended timestamps just isn't going to work for me. The author's got time to implement 11 different compression algorithms, but can't be bothered to put in support to store file attributes? I think his development priorities are a little skewed, IMHO.
And FreeArc is compatible with......nothing. And the amount of people and/or web sites I have seen using this file format......none. My friends & I would never use anything like this till the author gets the basic features in & I suspect most people are the same way.