Which characters you keep in storage & why?

I forgot to mention in my earlier post awhile ago that I had the beasts already stored (didn't want those random useless prizes from them when they complete their 4hr task), Monty Mort (wish I had not started that Vestige quest or not place the Academy Ruins), and Slithers.

I have one Non-Playable Character stored too that was from the Wild West event who came in one of those Black Friday Mystery Boxes last November.