I think the only ones I ever used were Razor Sun (Sunset Love) and Saito Mage (Ancient Pyramid) to Luciana, and Van Fang's Hell (Mad Man's Sun) to Sarah. I used Razor Sun early on against the Giants and such, and Saito Mage is obviously awesome. Van Fang's Hell is a pretty good all-hitting Fire attack, too. Another one of them teaches the pretty good spell "Ultimate Wreckage" (Hours of Doom), and Luciana learns that through leveling up, so I would teach it to someone else, probably Baretta. Although I've never used it, Final Mirror teaches "Vision of Death", which says that it inflicts all status effects on one target, which could be useful in certain situations. Other than that, I never really used any of the others, so I guess you would just experiment with them and see which ones are effective.