APL - without a shadow of doubt.
As with most programming languages, Perl has its uses. Personally, I think that it’s best used for short test processing scripts - a sort of user-friendly sed if you will. I had to maintain a application of tens of thousands of lines of Perl once - that was not a pleasant experience, and I wasn’t allowed to rewrite it in something like C. I had ample justification too, besides not liking Perl for large projects. The code was written by an imbecile who left ‘strict’ out because it made his code crash. It was unreliable and crashy, and still I wasn’t allowed to do the job properly.
The worst language I ever had to use was APL. I have a knack for picking up languages quickly, which meant that I’d often have to pitch in on eclectically coded projects. APL tested my abilities and patience and - although I got to be reasonably adept at it - I never want to touch it again. A vile waste of time, and not even as efficient and fast as its adherents claim. Every challenge that APL's fans have thrown at me to prove its mathematical prowess I have been able to beat on identical hardware just by using a sensible language. Like C. :-D