For me, that would be Argos. As controversial as he is, I feel he has the most potential for growth out of all the characters we have seen so far(prehaps even more than Storm) All the characters in Minotaur hotel are searching for a purpose and a place to belong, except him, who gladly flaunt it. Seeing how he reacts to the master, who in his kindness to Asterion makes him obsolete, will be so interesting to see. Will he cling on his intended purpose? Will he learn he can be more than that? There are so many way you can take this character and that really excite me for the future. Plus that scene where he hugs the master was really cute.