Arc is, arguably, simpler than either Scheme or Common Lisp. The only reason for learning these other languages first, in my opinion, would be because of the greater availability of teaching materials.
In fact, if there's any language I'd recommend learning before arc it would be Haskell. You'll enjoy arc much more if you have a good understanding of functional programming first. The best way to do that (although a pretty hardcore way) is to learn Haskell.
