I write in my head also. I then take the song to the guitar to work out the basic chordal arrangement. Sometimes (rarely) I hack it out on piano.

When I move to BIAB it is to make backing tracks. I usually don't mess with styles. Rather, I look for individual instruments that work. I will also play with alternate chords to see if I can mix things up a bit.

The whole of it then moves to Sonar to record live instruments and vocals. Sometimes I will replace the BIAB guitar track with my playing. Sonar is my DAW of choice because I've been messing with it since version 2.