I'm probably doing it wrong (again) :V
Well, the difference a character makes in scoring is directly related to how many bullets are available to be reflected to you (the more bullets you clear on your screen, the better your score).
Cirno has four advantages in this regard.
1) Her Lv. 2 spawns entirely from one point and spreads outward. Later in the match, there's a better chance that there will be an enemy of some kind right where at that spawning point, and every reflectable bullet will come your way. Yuka, Reisen, Reimu, Tewi, Komachi, Mystia, and to a lesser extent Medicine have similar Lv. 2s - with varying effectiveness. Since Cirno's bullets stop onscreen during her Lv. 2, they're more likely to get hit sometime.
2) The snowflake she shoots before the wall of icicles falls during her boss attack works the same way.
3) When using one of her Perfect Freeze spells, some of the indestructible bullets on your screen turn to snow bullets that you can wipe away.
4) Her reflected bullets are mostly slow.
The downside to Cirno is that her scope isn't good for scoring and her icicles are a little too good for keeping foes alive while she racks up points (not referring to Extra Mode here).
