I have tested a lot of distros on my first hard disk CentOS, Suse, Fedora,
Debian, Mandriva, Sabayon, Mepis, Antix Mepis and more and I still came back to
Ubuntu and Mint. I also tried some more (PcLinuxOS, Granular, Kanotix, Zenwalk,
Knoppix) but the older versions gave graphics problems.
To me Ubuntu is the best choice.
I have even tried older, dead distros (successfully), like Redhat Shrike and
Lorma Linux but Ubuntu and its derivatives are a lot better.
Unfortunately, Ubuntu seems to be the best one. Easy to use, fast to install
programs, large repositories. Great functionality. Easy to get the right answers
to the problems.