[science4sail]

(This is from my personal experience, your mileage may vary) Scheme and CL have different goals: Scheme aims for a quite minimal language with additional abilities primarily through libraries (part of the reason that it is often seen as a teaching language, the core can be learned quite quickly), CL seeks to be a more general purpose language, so it standardizes more features and abilities. Also, Scheme seems to emphasize functional programming more.

The choice of a Lisp seems to be one of situation, context, or religion (for example, see the disagreements as to whether a Lisp-1 or Lisp-2 is better).

Arc may just appear to be an attempt to build a better mousetrap (and is not CL), but it seems to be inspired by the same reason that created most other programming languages: someone (pg) decided that there existed a better way to do task x. I, for one, think that the syntax is cleaner.

I'm usually a Schemer, so I can't really recommend CL implementations...