I don't look at it in a technical light, but rather how do you wish to be shaped by the tools you use and create; and the people you interact with and learn from. For example, here's a short list of how I view the choice differential.
Use Perl if:
primary use unix, BSD, linux
care about portability and longevity of your work
prefer master of the language and workflow efficiency
are familiar with and like the Unixtm philosphy for tools
believe that a user community exists such that you tend to mastery (i.e., believe that iron sharpens iron)
see the value of an unbroken linkage to unix wizards of the past
not only comfortable with, but are actually attracted to the idea of being among a class of remnant working and toiling for the day that Perl will be rediscovered and appreciated
Use Python if:
primarily use Windows or are agnostic to the OS
don't care about the longevity or portability of your work