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7z is available in a command-line port that works on Unix-like OSes, including the Mac. Several front-ends are available, mostly just for unarchiving.
RAR is a proprietary commercial format and last I bothered to check, the developer wanted $30 per install of the official RAR-creation software (discount bundle pricing available) and had a bit in the license of the unrar program saying that its source was not to be reverse-engineered to create a RAR-encoder.
Zip is common, understood, at a reasonably stable point in its development, and readily available or portable to just about any OS, and there are plenty of tools from multiple sources to deal with it, which is a decided advantage over the other formats, even once one factors out the commercial proprietary aspects of stuff.
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