Who should I rank up?

HeroSeeker1

I am debating between taking my 5 star corvus (sig 5), 5 star starky (sig 50) and 5 star AA (sig 40) to rank 5 or my 6 star hulkbuster to rank 2. I only have 1 other rank 5 five star and that is Claire Voyant (sig 75)

TheLegend27

I'd go Corvus