The Advanced Packaging Tool (APT) was created to manage dependencies and upgrades for Debian's package management system known as dpkg. Originally, APT was used on the terminal with the simple commands (apt-get) to retrieve, remove,or upgrade packages.
Synaptic and KPackage are graphical programs used to manipulate APT for various purposes. While these programs simplify package management for graphical users, they in no way remove the underlying functionality and power of APT/dpkg, arguably the best package system in existence. Apt is such a fine tool that Connectiva created a port called apt-rpm for RPM based distros. However, the sheer size of Debian's repositories plus strict policies and thorough auditing of packages makes it a winner.
However, that's just my opinion.
http://www.debian.org/doc/manuals/ap.../index.en.html