Which one should use?
Depends on the unit
Let’s say a meta build Reinhardt.
Which one he rather have?
Moonbow because the units he wants to hit harder will have higher res he wants to negate
But like if it were a bladetome or something, you want Glimmer
Some units are used as non AOE nukes (Bladetomes, sometimes TA Raventomes), and they already deal out lots of damage, so amplifying it with glimmer is suggested.
But for general purpose wall breaking, Moonbow is preferred because it just lowers the enemies stats, and glimmer may not help if you are dealing less damage.