Farming for old republic or Jedi Training Rey and C3PO? Need some advice.

The best choice would probably be to forget about old teams like CLS and JTR for the time being and focus on the Revans, Separatists, and Galactic republic. Will probably give you the most return in both GA and elsewhere. Having old meta teams really just becomes a huge obstacles in GA, as you'll be matched against powerful toons vs powerful toons instead of overall GP, and old meta toons count toward this same as the new ons, meaning that if you have say CLS and JTR, you'll be matched against a lot of JKR and DR, GG, Padme, etc.