RAR generally gets better compression than ZIP, but ZIP is free and open source. Both RAR and ZIP use LZ77 compression, which has the property of decompressing very fast. ZIP uses a straightforward structured format to store files. Each file is...  moreRAR generally gets better compression than ZIP, but ZIP is free and open source. Both RAR and ZIP use LZ77 compression, which has the property of decompressing very fast. ZIP uses a straightforward structured format to store files. Each file is individually compressed using DEFLATE or another more modern compression algorithm. (Recent versions of PKZIP support LZMA and several others.) Then, each compressed file is appended to the ZIP file, and a directory that lists the files and their locations in the archive is appended to the end. WinRAR has a trial period and eventually you pay for it.
7-zip, I believe has a free version and a paid version.  less