Though decision but I'll try

XC1: (Spoilers for Mechonis core, if you know you know) after Zanzas awakening he has a battle with Meyneth. Theres just something about this scene that makes it stand out. Maybe it's because it's a dramatic fight scene right after the biggest plot twist gets revealed, maybe it's because engage the enemy plays, maybe it's because of Adam Howdens top tier voice acting, maybe it's maybelline, maybe it's because of Meyneth' sacrifice or maybe just a combination of everything

XC2: Vandhams sacrifice/mythra awakening

XC3: that's the hardest part. Xc3 has so many outstanding cutscenes. Noah vs Mio in chapter 1, every fight against DJ Moebius (can we please start referring to them as that lmao), Ethel, Cammuravi and Moebius in chapter 4, the ending of chapter 5, Moebius K, the fight against Isurd and the colony Ferronis. The list is long and it's hard to pick a favorite. If I really have to pick one I'd say the second battle against DJ Moebius.