Vader or Thrawn?

I run Palpatine, Sion, Nihilus, Thrawn, and dark Bastilla in arena right now.
My question is this. Should I replace Thrawn for Vader? Every team I fight that has dark Bastilla has my same team but uses Vader instead of Thrawn. Is that the best team with dark Bastilla? I know Vader is a great toon, but Thrawn is just so good.
Note: I have both Vader and Thrawn uniques zetad.