My vote is for the ActiveState distribution. The main reason is that PPM means that you tend not to need a compiler to install many of the common modules. Obviously there are some modules that require a C compiler but they tend to be less mainstream and some of the repository maintainers take requests so they can do it for you if you ask nicely!
The one thing that I would point out is that the PPM builds on ActiveState are built automatically and need to pass all of the tests before they are released. I have noticed that some of the modules are at quite old versions compared to CPAN. For example - Activestate has a much older version of WWW-Mechanize than the University of Winnepeg.