Slackware is still the best for adherence to the old unix style. It dosn't hold your hand for you, like Ubuntu. Ubuntu is heading for the HandHeld market, so their desktop is cumbersome for someone used to a full featured desktop.
in reply to Which is the recommended flavor of Linux to learn perl?
I also note that Ubuntu's package manager Perl module support is a total mess of use of split module names. If you go with Ubuntu, you would be best to install all Perl manually.
Ubuntu is easy to install and get help with, whereas Slackware requires you to figure
it out on your own.
FWIW, I also like Linux From Scratch and Gentoo , mostly because they have excellent docs for installing various system components.