WinZip applications, which create Zip files (.zip or .zipx), allow you to choose between two different compression methods. The Legacy method creates Zip files that are compatible with almost every other Zip file utility, but the compression used is not likely to create the smallest Zip files possible. The Best method alternative uses compression that will create smaller Zip files (usually) with a .zipx extension, but this method will not be compatible with all Zip file utilities.
.Zip Legacy compression (maximum compatibility)
The Legacy (Zip 2.0) compression method, which creates .zip files, uses a traditional data compression algorithm, known as deflate. Deflate is supported by all versions of WinZip and virtually all other Zip file utilities. The deflate method is generally considered to be a good, all-purpose compression algorithm for use with most types of files. .Zip: Legacy compression is your best choice if you will be sharing your Zip file, especially if you do not know what Zip file utility the receiver of your shared files will use or if you already know that an older or limited utility will be used. WinZip applications use the highest deflate method setting available, which is maximum deflate. Using WinZip, your .zip files will be easily unzipped and they will be as small as possible for this compression method.
.Zipx Best method (smallest size)
The Best method option allows WinZip applications to choose a compression method from those available in the application for each file. The choice is based on the file type and is usually the method that will compress that type of file the most. .Zipx: Best method should be selected if compressed file size is a primary concern. If you plan to share a .zipx file, please make sure that the receiver of your shared file is using the latest version of WinZip or another Zip file utility that is compatible with all of WinZip's advanced compression methods.
Increased Control - WinZip ribbon compression options
The WinZip ribbon provides another level of control. In the Zip tab, you can choose a different compression method for WinZip to use when creating .zip and/or .zipx files. These compression method settings will by saved when you close WinZip so that you will not have to make the change again. If you want to use a different method later, you can change settings again.
If you have any questions about this information, please submit a Technical Support ticket.
Default compression - What it is, how to change it
Additional Compression Methods Specification
Is WinZip compatible with older versions of WinZip and other Zip file utilities?
What registry settings control WinZip's Default Compression?
WinZip Courier Attachment Options