I always do it like this: dantooine, nar shadaa, dxun&onderon, korriban and obviously back to dxun&onderon. I do it like this because I always want to get my crystal first and early on so that i can get it to the highest level possible. then I go to nar shadaa cause I want to get hk-47 quickly as well and I get almost every other character there except for mandalore.