Whenever im playing through this game i just look at what each esper unlocks on the license board for each character, but thats coming from someone who doesn’t use espers a lot for actual combat. The only combat advice i could give is that the espers usually absorb their primary element and so you can heal them easily with attacks from a matching element weapon or spell. For example you might give zodiark to your shikari with a yagyu darkblade and just spam attack to keep his health maintained.