In light of Ovid's recent meditation, I think the only way to really settle which is the best Perl book, is to put it to a poll :)

Here is a list (mostly) taken from that thread:

Update: Suggested Poll Title: If I could only own one Perl book, it would be:

• Learning Perl
• Perl Best Practices
• Perl Testing: a Developer's Notebook
• Higher Order Perl​
• Programming Perl
• Perl black book
• Perl in a Nutshell​
• Object Oriented Perl
• Effective Perl Programming
• Perl Cookbook
• Learning Perl Objects, References and Modules

(Apologies if this one has already been done - but I couldn't find it, so I guess not)