Packaging and ecosystem has changed a lot recently, so On Lisp or ANSI Common Lisp would both be outdated quickly (as would Seibel’s PCL; PG does not have a book with that title). Most of that you can find online: practically everything is available through Quicklisp and it’s a very intuitive piece of software. Concurrency is harder and Bordeaux Threads might be too new for detailed inclusion in On Lisp or PCL.

I would highly recommend On Lisp once you have gotten the syntax down. I ordered a printed copy of the PDF (legal since PG released it) and have been working through it. On Lisp won’t show you things that are easily done in other languages; its goal is to teach the power of CL. Certainly by the time you’re done you’d be comfortable with many types of macros, closures, the REPL-based workflow, and other strengths if CL, able to find more about how one uses it in practice without much trouble.