what's the best type of music to play while driving?

A lot of that depends.  I mean, if I'm by myself, heck - anything I like to sing to!  But it gets more complicated when I am expecting company in the car.  Certain people don't like certain singers, types of music... whatever.  Some people don't like music.  I'm a nice driver, and I try to accommodate.

Then I have my playlists.  The "Rain" playlist, sporting songs like "Rainy Days and Mondays" by the Carpenters and "Rain" from the musical, Once on that Island.  When I'm in a bad mood, the "Sad Songs" playlist comes up, with "Sad Songs" by Matt Nathanson and "40 Kinds of Sadness" by Ryan Cabrera.  In the rare even there is a child present - do not fear!  I have my Disney playlist with everything from "Thomas O'Malley" from The Aristocats to "Portobello Road" from Bedknobs and Broomsticks.

Then, when in doubt, there's always "Chariot" by Gavin DeGraw and "Uncharted" by Sara Bareilles.