The best file archiver (zip/unzip tool) for Microsoft Windows is 7-Zip. It’s open source, fast, free, and highly recommended by sites such as CNET and Lifehacker. I use it at home and work and recommend it to others.
Modern Windows, at least Windows XP, has built in zip file support. If that’s all you use and you don’t run into files in other compression formats, then you don’t need a separate file archiver tool. Most of us, though, want something better than the basic built in functionality and many of us sometimes get a file in .rar, .tar, tgz, or even 7-Zip’s own .7z format. You can buy WinZip or another paid tool, or use one of the other free tools, but I doubt you’ll find a better overall tool than 7-Zip. The fact that it’s free and open source is just icing on the cake.