Board Thread:Question and Answer/@comment-76.184.23.252-20140826032210/@comment-10117350-20140826043840

It really depends on which cards you're talking about and how much you need the space / medals right now.

Out of the two cards you mentioned: These two should be traded for medals since they are not particularly strong or useful (as SR cards anyway). However, if you do medal them and Nubee decides to bring them back, you'll need them to drop two times so... it's up to you. Honestly though, if you don't like their art there is no reason to keep them. Also, I don't think Nubee will bring them back anytime soon.
 * Destroyer's skill is just yet another "250% damage to all / 15% chance" and if you got HSR Yosakoi two events ago, you already have a better AoE Passion card.
 * Matrix on the other hand, has a skill that is more "unique" (as in, not as common as the AoE damage) but it isn't a good skill.