For me, it'd have to be Fleeting Words. It's then a hard choice between the Weiss edition and Another Edit. I just really love it (and also that entire storyline).

Shadowlord, Exhausted 3, The Final Song, Song of the Ancients Devola, Wretched Weaponry Dynamic, The Tower, and Seere's Prayer are also really great, and I think an underrated one is Cold Steel Coffin. Still waiting on an official piano Cold Steel Coffin...