Extra Difficulties:
EoSD: Easy stage, difficult boss, requires more skill than memorization
PCB: Easy stage and boss, but requires a lot of memorization
IN: Easy stage and boss, a few short segments that require a lot of skill
PoFV: wut
MoF: Very easy stage, easy boss, most forgiving bomb system
SA: Somewhat difficult stage and boss, and most unforgiving as well
UFO: Difficult stage, very easy boss, but requires skill to maximize lives/bombs during the stage
So yeah, Suwako's stage takes the least amount of real dodging skill, and when you screw up, you can bomb and regain the power after 1 or 2 attacks. PCB and IN extras are pretty equal to me, so after MoF, do whatever seems funner :V