How would you rank the characters from easiest to hardest for the extra? It's one of the ones I still need, but UFO just destroys me, so I'd rather just do it once with a good shot type. I have SanaeA cleared right now, but a friend's told me she's a terrible shot, so I'm not sure.
SanaeA is competent for most bosses, given that you can be away from the boss at times and still deal rather good homing damage. Particularly in Green and Rainbow UFOs, where you might not be directly under Nue (and Guerrilla Typhoooooon) . Her bomb lasts awhile and gives full speed movement, and also is a full screen clear and the invulnerability ends right when the bomb stops so it's good for LFO and Nue.
Terrible shots include Marisa B. And MarisaB. But ideally you play the game first with MarisaB, fail, then switch to a not-terrible shot and win on your first try.
Ranking wise~
From easiest to hardest
SanaeB for being able to blow up UFOs almost immediately.
ReimuA for brute force
MarisaA for lasers and being second strongest
Note that the above three are very close to each other in rank.
Then, SanaeA is slightly harder.
ReimuB isn't as horrible as people say she is, but she's not gonna kill quickly (notably, her bomb can deal damage after your invulnerability ends, so it does damage to Nue!)
MarisaB can get shotgun damage during Surprising Slash and Undefined Darkness, maybe, but she's probably dead last.