Birth By Sleep - Chock-full of great original music. Yeah Ven's theme is just a thinly veiled theme of theme of Roxas, but the plethora of original worlds brought with it brand new music. Definitely the puzzle-piece that makes this whole triple-soundtrack enjoyable.
358/2 Days - Slightly more fleshed out than Re:Coded. Most of the original songs are pretty much just modifications of songs found near the end of KHII though.
Re:Coded - Little new original music and repetitiveness lead this to be probably the most boring of the soundtracks... Very reflective of the "not relatively important to the story-line" vibe that comes across while playing the game itself.