Perl, hands down, if only for the incredible resource of CPAN (http://search.cpan.org/). The benefit of using a scripting language with such a massive contributing community is that you are unlikely to ever need to invent something yourself.
Perl also has the benefit of being as complex as you need for the current situation. You can treat it as a simple scripting language for quick administration or single purpose scripts, but you can use object oriented concepts or extensive meta object systems when you want to create larger, easy to maintain applications (like daemons, servers, clients).
The differences among the scripting languages alone aren't severe enough to pick a clear winner, but you should primarily look at how easy it will be for you to find information on topics you care about.
Perl syntax can also be strikingly close to C, as long as you can get around the lack of typing and the sigils; advanced perl use would come naturally as you eventually learn the strengths of the language.
And for naysayers on the readability front: you can write hard to read code in any language. If you look back at your code from 4 months ago and can't understand it, you're doing something wrong.
p.s. This post was filled with links to various administration friendly modules on CPAN, but apparently new users can only post one link, so use that CPAN link to search for things like 'CVS' 'SVN' 'Cron' and 'Moose' (an extensive object system)