DC & Marvel: What's the Difference?

What is the difference? I think, with Paul and Jim each producing a thoughtful piece regarding DC Comics, it's got me thinking about what it is that makes people prefer one company over another.  I've never been able to put my finger on what it is about DC that feels one way, and what it is about Marvel that feels another. Also, I realize that there are other comics out there, being made by other companies, and if I had to choose one superhero book right now, it would be Invincible, and that d