There are a few problems with 7zip. It's extremely slow, it isn't widely accepted yet (at least compared to Zip, Rar, or gzip on *nix), and often times the difference in size between it and winrar are negliable, if anything at all. Though, there were a few times in my test experiments when 7zip blew everybody else away which impressed me, but not enough to switch.
When I am on Windows, I use Winrar. Quick, good compression, and most people are already setup for it. When I am using Linux and only intending on working with said file on Linux gzip is the only way to go. Why? Because the compression is decent and the speed with gzip on *nix is sick. (I've compressed 1GB text in 3 seconds, reducing it to around 150MB) Now, if the file is going to be spread among different people and different platforms I am forced to use slow, bloated zip. The reason being is it works easily on Windows, *nix, and MacOS.
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