I'd be interested in if you considered Guile first and what made you decide in favor of common lisp. Few years ago when I decided its finally time to learn lisp I looked at few variants and Guile seemed to have the benefit of: fairly vibrant(but somewhat hermetic) online community, a sizable manual that describes most frequently used APIs (you can learn the language itself very quickly, but it's the knowledge of the APIs you need to do anything in the "real world"), and being actively maintained and extended. So I chose Guile.

For those that don't know these terms Guile and common lisp are two implementations of the same scheme language (simplifying a lot).