Which Mystic 5* to Rank up?

PandoraFlame

I only have two Mystic champs that are 5*, and I realize that I am almost able to rank one of them up. They are both at Rank 1 as of now, possibly going to Rank 2

PandoraFlame

Or should I wait and save for 2 Tier 4 Basic Catalysts and 3 Tier 4 Skill Catalysts to rank up my Thor (Ragnarok) 4* to Rank 5