ReimuA: 9/10
Overall the best shot in the game, great for survival on all difficulties thanks to her strong focus shot (knocks out bosses fast), small hitbox for dodging (shared with the other Reimu shots), and gapping mechanic (as ZM said, only really useful in a couple spots, but it's there if you want it). Her bomb has a long duration, which is great for getting past difficult attacks with proper timing, though it only does good damage when combined with her regular shot. Her bomb also lets you graze optimally without destroying bullets, but the effect only really becomes the most pronounced on Lunatic and Extra - MarisaA and B currently have higher scores everywhere else. ReimuA's only weaknesses are having the toughest Satori fight and her lack of spread, which is still only a problem in a few areas.
ReimuB: 6/10
Perhaps a bit underrated by some in the past,, this shot's homing capability, while weak, is still useful at times to widen your range a bit. Notably, her wisps also pierce, which makes them useful against a handful of Orin's attacks (i.e., second Stage 4 midboss attack, first Stage 5 boss card), though their homing ability might screw this up elsewhere. Her bomb isn't particularly useful for survival on lower difficulties outside of the invincibility it grants, but it can be placed away from bosses so you can graze right on top of bullets' spawn points, which is better than nothing in terms of scoring. Her special ability is pretty redundant when you can simply go up to the PoC on lower difficulties (few bullets to stop you, after all) or graze lots of bullets on higher ones to max out the Communication Gauge.
ReimuC: 5/10
This is the shot type for those who like to bomb their way through everything, as that is ReimuC's greatest strength. While not good for scoring because it follows Reimu and thus deletes bullets nearby, the plethora of bombs you can collect throughout the game makes maintaining a good supply feasible. Reaching what is essentially max power at a distance at 3.00 Power might be considered a strength, but her shots are even weaker than ReimuB's. However, this does make using bombs at full power more practical since her shot damage won't be decreased, not unlike MoF's shots. Her rotating option mechanic is useful during stages to pick off enemies on both sides of the screen, but it places a bit of an undue burden on unfocusing even for a brief moment, which could screw up your damage against bosses. Her increased speed when not pressing any buttons doesn't contribute a whole lot to either scoring or survival.
MarisaA: 7/10
While this shot is unusual in that her shot archetype is reversed (forward shot while unfocused, spread shot while focused), maintaining good damage from a distance is still something you can get used to with practice (think controlling Youmu solo in IN to have her option hit targets as a "human"). Her forward focus shot deals nearly as much damage as ReimuA in most circumstances, and having a spread shot alongside that gives her survival utility during stages as well. Her having twice as many bombs I find to be a mixed bag, however. This does allow you to give yourself invincibility at more individual points, but they have half the invincibility time and attack duration as other bombs. Damage from her bomb also depends on how well you place it - by itself it's very weak from a distance, but it does deal ReimuC levels of damage when shotgunned. As with ReimuB, her bombs can be placed away from where bullets spawn, which helps with supergrazing. Regaining the equivalent amount of power from bomb usage (as in, 2 of MarisaA's for 1 of everyone else's) is also slightly more difficult from a mathematical standpoint since Power items don't give her twice the power to compensate. As with the other Marisa shots, her larger hitbox becomes an unusually prominent issue for survival on Lunatic and Extra, where attacks can get really dense.
MarisaB: 8/10
Second-best shot in the game because of her sheer versatility and good scoring potential. Getting used to switching between certain shots does require a bit of practice, but not as much as with MarisaA. Her five shot variants let her deal with both stages and bosses quite effectively if you know how to use them. She has an almost excessive amount of spread for stages, which lets her utilize the PoC and CG from pretty much anywhere on the screen. However, she doesn't deal as much damage from a distance, since her dedicated forward focus shot (Fire) isn't any stronger than ReimuB. You have to shotgun enemies with Wood, Earth, and/or bombs to kill them fast, which can make bosses trickier on higher difficulties if you just spam this strategy. As with ReimuB and MarisaA, she can place her bomb away from targets to help with supergrazing - the combination of this and her many spread options makes her the best for scoring on Easy, Normal, and Hard.
MarisaC: 3/10
This shot doesn't really have much going for it. Her bomb is her most useful aspect because of how defensive it is - it functions like a Supernatural Border from PCB, though you can't pop it manually once it's out. Getting 0.50 Power back if you survive its duration is a nifty bonus, good for new/intermediate players who are still getting used to survival on any difficulty. However, her bomb has pretty much no scoring potential. Her shots deal intermediate damage from a distance, which makes her more useful against bosses than some others in terms of pure survival play, but her shots have no spread and lag noticeably, which makes it difficult to hit moving targets (while some of Marisa's shots in other games also have lagging shots, I think this honestly went out of style years ago). Whatever strengths she has tend to fall by the wayside once you get into higher levels of play and/or start getting comfortable with the other shots that are trickier to use, to say nothing of ReimuA being better in just about every way.