7-Zip Advantages vs. Disadvantages:

Advantages
7zip is free of charge and for many users that could be the decisive attribute. It has its own archive format 7z that in many cases is the best format available. 7z is a self-extracting archive format. It has a 256-bit AES cipher. It is an open source program. Has a command line interface. It scored highly in many review sites. Compresses and sends to mail by 1 click.

Disadvantages
For some people the interface is not friendly enough (I personally disagree). It can only unpack RAR files.