This is a topic that is very subjective, so take my answer with a grain of salt

Advantages to learning Perl 6 over Perl 5:

• Often the error messages are better
• Many concepts are easier to learn (for example much easier OO, fewer edge cases with closures)
• Much better support for asynchronous and parallel programming
• Up-to-date books (around 8 books released in the last 18 months or so)

Advantages to learning Perl 5 over Perl 6:

• More material online
• Broader user base
• More stable, and usually faster by default
• Broader module base

Pick your poison :)