Both languages are very similar, and if you are just starting out, then Ruby is probably easier to learn than Perl.
But if you have a specific area that you are aiming for, it probably comes down to the fact that there are better libraries in that area. And in matters of the breadth and quality of libraries, Perl wins almost all the battles over CPAN . Take a few minutes and find the types of libraries you are interested in and compare them with what you will find on Ruby Gems.