Recommend next Zeta

I would do Thrawn, or maybe Sion.

Honestly, it depends on:
1) What aspect of the game you want to improve most (a specific raid, arena, PvE, etc)
2) What squads you already have built.

If your nightsisters are terrible, then Ventress' leadership would be wasted right now. Same with Thrawn - if you never use Chimaera, or use him in your arena squad, why would you spend a zeta there? We need more info to help you more effectively.

Sion if you run zPalpatine leader.
Post your swgoh.gg if you have one( if you don't then you should probably make one)

Here is my page. https://swgoh.gg/u/swamptours/

Looks like you've been switching around your 5th member on your Arena squad. I'd say you should make your 5th be Sion and put the zeta on him.

Depends on what team you are going for. R2's number crunch and raid han are solid choices, i have both and they are amazing, but if you are going sith in arena put the zeta on them.