Tough call. Chewie and C3 is was really made CLS relevant again.
Both Palp and CLS w/out new legendaries are both old metas. EP is less old, and might get you a little further. CLS and his team use a few toons that are also raid viable
If you go Sith, I recommend Palp's second zeta, Sion's zeta, and CLS IBAT. IMO Palp lead and Sion's are the big zetas on this team.
If you go Rebels, I recommend CLS IBAT, Either of R2's, and then R2's last zeta or Sion's Zeta. I recommend running- CLS, R2, Thrawn, Solo, GK/Old Ben
Nothing wrong with saving a zeta with either option. CLS IBAT is always good and Sion's Zeta vastly improves him