All three of Ruby, Python, and Perl are good for quick development, prototypes, and web apps. I'm guessing from your question that the most substantial part of this project is the AI piece. Perl does have quite a number of AI-related libraries on CPAN. Check out the AI namespace for a sampling. There's also modules in other namespaces so make sure to search for specific things like "Bayes" or "SVM".
I don't know much about the AI library options for Python or Ruby. My recommendation is to take a day or two and do some serious research on the libraries for each of Perl, Python, and Ruby. Since you've already used Ruby before, if that has the libraries you need, it's a no-brainer, and Ruby is certainly web friendly.
As far as the web side goes, for Python, I've heard many good things about Django. For Perl, I'd recommend taking a look at Catalyst.
You'll note I've ignored PHP. That's something I try to do as much as possible ;)
