The Midi packs are great for manipulating rough ideas into workable tracks for recording.
I like to create the core of my idea and then place the midi into EZkeys. From there i browse EZkeys Midi files and convert my tracks into something more exciting.
Pros) with the same midi pack you can get endless amounts of sounds. You're only limited by your creativity on actual keyboard.
Cons) EZkeys itself only has a limited set of instruments per pack. Most DAWs have a wider range to choose from even in there basic packs, but they don't give you the same freedom as EZkeys.