Hey dude, some more information would be fine. Are you in a hAAT guild, do you play heroic rancor?
If both can be answered with yes, I would suggest a General Kenobi / zeta Barriss Team, because it is a very little invest for a huge outcome. Since you are working on Phoenix, you will be ready for Thrawn nevertheless. So I would start getting Nihilus from the shipments until 4*. More ist not needed for arena.
And I would continue working on my empire, getting them ready for R2.
So my team would be Kenobi, zeta Barriss, zeta R2, Thrawn and Nihilus (2 zeta needed --> Rank 1 every day)
If you are not in a hAAT guild, this question can not be answered that easily. I would get Rex as soon as possible and I would get ready for Commander Luke. Maybe he will be back in february or march. And I would start working on chaze... they are kind of outdated, but I still use them on a 1 year old shard and I fight for Rank 1 every day.
So I would suggest something like:
Rex - Chirrut - Baze - R2 - and on fith you can chose from zeta Han, Nihilus, Thrawn
or, if you want to wait til CLS return something like:
CLS, Old Ben, R2, Raid Han, Thrawn.
All those squads should be Rank 1 viable.