Moved to rancor raid.
Your R2 and GMY aren't 7* yet, so if you are looking at heroic, I wouldn't necessarily preclude having Thrawn before too long either.
Teebo and Jyn are both good rancor toons, but Jyn is a longer farm. Likewise Rex can take a little longer. Qui-Gon is another easy farm that has tmr on basic, and can help you if you want to finish Yoda. If you get R2 to 7*, he works well with Teebo to keep him stealthed.