Cards are very interesting. Most of them are really bad - Talis, Mahu, and the Section ID Cards fall in this category, and Dancing Hitogata is a without a doubt one of the worst items in the game. Syringe, Amore Rose, Kunai and Kan'ei Tsuho might have some use, but they are (very) niche at best.
This leaves us with Gal Wind, S-Ranks Cards and Guardianna, which all are useful in their own ways.
Gal Wind can be used to easily trigger Mag invincibility.
S-Rank Cards I don't really have much experience with but from what I've gathered, they are difficult to handle, but useful nonetheless.
Guardianna, however, is one of my favourite items in the game. It is extremely underused and not only has good base ATA, but also can do massive damage thanks to its Spirit special in combination with the triple hit at the end of the combo (which makes the last hit really devastating). Also, it can kill Dubswitches and hit enemies in the Air (like Dragon), making it a very handy tool for soloing and the like. Seriously, try it out if you get the chance!