I have been using 7-zip for years as my default archiver, it is fast, it unpacks zip and rar files, and compresses into .7z files much smaller than similar zip or rar archive.

However, I just discovered NanoZip which although in early alpha is truly outstanding with decent compression speed and much smaller files than 7zip. So head and shoulders above zip and rar. The interface is still clunky but if you have an urgent need to fit more data into a small amount of space try NanoZip.

For more info check CompressionRatings.com and MaximumCompression.com.