Next 5 star to rank 4 based on my roster

Kamr05

All of my current r4 champs were ranked up a while ago. I only pulled Stark Spidey, Medusa, Domino, Ghost Rider, and Blade in the last few months on a very lucky streak.
I'm already Uncollected, got Elders Bane, done Varient 2. I'm torn mainly between Medusa, Domino or Stark Spidey, I love all 3 champs but wondering which will benefit my roster the most. Any help would be much appreciated, thanks.

Kamr05

Just to add I'm in the middle of unlocking the rest of the suicide masteries. I grind arena a lot now so I prefer having suicides on for that.