WinRAR and Winzip need paying for (eventually), 7zip is free and does the same thing. That’s it really.

You can use 7-Zip on any computer, including a computer in a commercial organization. You don’t need to register or pay for 7-Zip. But you can make a donation to support further development of 7-Zip.
The main features of 7-Zip

* High compression ratio in new 7z format with LZMA compression
* Supported formats:
o Packing / unpacking: 7z, ZIP, GZIP, BZIP2 and TAR
o Unpacking only: ARJ, CAB, CHM, CPIO, DEB, DMG, HFS, ISO, LZH, LZMA, MSI, NSIS, RAR, RPM, UDF, WIM, XAR and Z.
* For ZIP and GZIP formats, 7-Zip provides a compression ratio that is 2-10 % better than the ratio provided by PKZip and WinZip
* Strong AES-256 encryption in 7z and ZIP formats
* Self-extracting capability for 7z format
* Integration with Windows Shell
* Powerful File Manager
* Powerful command line version
* Plugin for FAR Manager
* Localizations for 74 languages
Download Here