For me it's
https://youtu.be/S046VBHkQ-8
Plays only once, and it's during one of my favorite Servant fights. Hardly impactful in terms of LE EPIC BEAM FIGHTS but the way Avenger's frantic style of combat is explained and articulated is 10/10
>>717133561
It's very heartfelt, and the fact it's the only piano-centric track across both VNs to have such a positive tone makes it all the more special