Perl's driving motto is "There's more than one way to do it." Because of this priority and the huge archive of Perl modules on CPAN, Perl is an incredibly useful tool for building quick one-off scripts or hacking together tools in a very short time. However, it also means that it's very easy to write Perl code that will be impenetrable six months down the road. Perl provides very little assistance to someone who wants to write complex systems clearly. Features like perl -w (warnings), use strict, and Perl's module support help maintainability, but it still requires a great deal of care and discipline.

Python's support for maintainability, on the other hand, is excellent. Python's rich collection of modules and the fact that it's an interpreted language allow relatively fast development, if not quite as fast as in Perl. Generally, the more complex the system you're trying to build and the longer you expect to use it, the more potential there is for gain in using Python over Perl.

Personally, when tossing together quick one-offs or scripts that are very regular expression-heavy, I use Perl. Perl's regular expression support is so fundamental to the language that it's worth it, and its Swiss-Army-knife nature is perfect for things I don't expect to need again later. I also tend to use Perl when I want to write a very portable script, as most Unixes include Perl as part of the base system these days, whereas Python, while just as portable, tends to need to be installed seperately. When I want to build more complex scripts or larger systems, and maintainability is thus a higher priority, I use Python. I often use Python even for smaller things if I intend to keep them around for a while.

In the end, of course, it comes down to a matter of personal taste and judgment. Personally, I value being able to understand my code six months (or six years!) down the road far more than having every tool imaginable at my fingertips, so I tend to lean towards languages that help you write clear, readable code, like Python.