There is no best installer, only a best solution for specific demands:
apt-get is very useful for installing packages from the repository.
dpkg is useful for installing downloaded .deb packages.
I have no experience with synaptic.
There is yet a fourth program which you may like to use: rpm, which is useful for installing downloaded .rpm packages.
However care is necessary with rpm to avoid dependency conflicts.
For more knowledge google apt-get, aptitude, synaptic and rpm. You'll be amazed by Google's output.