Okay, I am not an Illustrator user (have inkscape) so I cannot comment on whether or not Inkscape has anything over Illustrator, but my understanding is that they are quite simular except Inkscape is open sourced and free. My suggestion would be that seeing as you already have access to Illustrator, to master that tool (or at least get comfortable with it) before moving on to others like it. And to answer you question about mapping with either, I have seen great maps made using both, either used exlusively or as a tool for the line work and brought into another prog for finishing.