Glimmer or Moonbow? Need some advice please

Not sure, I would say of these S!Camilla might be the only one here who wants glimmer? But I could also see her still using moonbow.
Like, Bridelia usually does like 15 damage per hit on tanky units, so 7 more damage isn't great, but on the same unit, Moonbow probably does like 10 damage. Not a super big difference but it's nice.
TA Camilla usually does a lot of damage to enemies she wants to be attacking, probably getting like 15 dmg on average off glimmer on decent matchups that she likes attacking into.

I would say it's also great on Bladetomes. The thing is, glimmer makes your good matchups better and your bad matchups worse compared to Moonbow, so I feel like it's really only good for Bladetomes.

I'd say Glimmer for SCamilla, as she's a TA unit, it helps solidify some kills.

Moonbow for Takumi, his Atk is too low.

Bridelia can go either way, depends on your build. Glimmer is probably your best bet though.

Glimmer works best on units with very high attack that you hope to get kills with in a single hit, like TA+Raven and Blade tome mages, so absolutely give it to S!Camilla. It's best on these because they can easily be attacking for 60+.

For Takumi it's a waste, since his attack isn't that high. For B!Cordelia I'd say it depends but suspect it's never worth it on colorless units since they don't hit effectively. If you're running her with Brave Bow+ you should use Luna or you're losing damage for no reason. Otherwise I'd say it again goes back to the question of are you taking it to help 1-shot a fast squishy unit that you can't double or to kill a bulky one in 2 hits. Moonbow approaches Glimmer in effectiveness and eventually exceeds it as the enemy's defense grows. If they are not close to death after 2 attacks, it means their defense is probably high enough that Moonbow will do more damage. If their defense isn't high enough for Moonbow to win, chances are it's close and either one would get the job done equally well.

The only time when Glimmer is actually better than Moonbow against enemies that you double is in the case of very high HP and low defenses. In practice, this is only relevant when hitting low resistance armors with magical damage.

Well, if you just want to take the math in to consideration, things are like this:
For moonbow, you need to take your possible foes in consideration. If you take a basis of the 38 top tier characters in the current meta, they have a standard of 25.73 defense and 24.43 resistance. The values for the rest of the heroes shouldn't go too far from that, so moonbow would be dealing about 8 extra damage for physical units and 7 extra damage for magical. Take in consideration that resistance is somewhat more balanced between characters, while defense is very high in just a few, so a physical moonbow user is likely to deal around 10 extra damage against a few characters and 8 or less against many. Also consider that moonbow is a way to beat enemies that you normally couldn't beat, so thats important.
Glimmer on the other hand works based on both your attack and the foe's respective defense or resistance (except for the distant counter on dragon stone users, in which case glimmer is awesome by default)
If you take a character with 50 attack power for example, glimmer would give you about 12 or 13 extra damage points as a standard.
Just remember that if you're facing a foe with extremely high defense or resistance, your glimmer could end up doing nothing.

I say S!Camilla with glimmer, Takumi with Moonbow, B!Cordelia it depends on your build, but i prefer Luna wih Brave Bow- she is beast!
I am not really a fan of glimmer it is like trying to win more, where Moonbow or Luna can save you.
Only time where i see glimmer as good choice is when enemy have massive HP and almost non existent Def/Res