Ableton Live & Push for music programming:
I discovered Ableton Live after having been a long time Pro Tools user. The interface seemed more intuitive and encouraged "in-the-moment" creation in a way no other DAW had achieved yet.
Flexibility, simplicity, and workflow:
I worked in the studio for a producer at a second computer running pro tools during live tracking sessions. I'd compose parts and sounds on our 2nd music programming station while the session musicians tracked right next to me. After a couple hours hands on with session view in Ableton, I completely switched over. It gave me flexibility and drastically increased my workflow. Also, it made it easier than ever to loop and work on certain sections of the song quickly so I could feed parts over to the main tracking computer.