4★ base Memory Gems already have the advantage of having higher stats compared to 3★ or lower, but the ones in AA tier give a pretty good easy or unconditional buff to increase damage.
Sword from Above is great for mages that rely on their skill as their primary damage, but it's also good for most characters in general.
Machine Golem Shuffle! are for characters that have high ST damage or can build up their ST pretty quickly, especially if you have a 4★ that is +1 unleashed.
Little Spirit Faye increases the already high MSM's burst damage even further. This shines more depending on how quickly you can build up MSM by using more +1 4★ unleashed Allies, matching element of paired allies, etc.
Aim for Wind Acorns is more conditional compared to the others, but it's a great Memory Gem to have to boost Wind element.
Rulers of the World gives a decent way to regen some MP, making it good for a prolonged battle. Its effect is similar to a Memory Gem that you can get for free, Briarborough Faerie Boss, but Rulers of the World gives more stats due to higher base rarity.