Which champion should i rank up

_Wiksi_

I wonder who should i rank up:
-Valkyrie
-Nimrod
-Scorpion
All of them are 5* and i have only mystic and tech awakening gem.
Category: I want a champion whos decent in story (i’m currently at 6.1.1) and bgs

HSS75

try researching about them, but i'm recommending ranking up Nimrod since he's a really good tank with shock damage and he destroys annoying mutants