I saw the other thread and thought I would start a parallel discussion for Mac users.
I switched recently and need to make a decision as to which to land on, having used both a little bit, but not enough to make a good decision. Here's my impression, but I've love to hear from guys who know both (if any such people exist).
1) Logic is a more complete package and provides a great set of instruments/synths out of the box, although most—excluding the fantastic synth Sculpture—could be replaced by some better third party product if money were no object.
2) DP6 is better suited to composition in terms of its controls for MIDI and even audio.
I could be wrong about either of those statements. My main focus is orchestral composition/soundtracks.