I was in same situation as you a month ago after nix team to palpy team. I started play dec/17.
I used boba for awhile and switched to thrawn when thrawn abilities and gear was max for my lvl (about 75). On my shard many nightsister teams and hes execute helped with remove taunt on zombie and ability blocks on the sisters. But in long run thrawn was better for me exept sister teams with week zombie couse you cant fracture those, ( they die).
Depending on your shard and what you fight most is the toon you pick for 5th slot. You probably end up with 2-3 toons for 5th spot and alternate between em depending who you fight.
