I remember reading that the consensus was Lumi first, then Barriss eventually. I 7*-ed Lumi early, while Barriss languishes near the bottom of my roster (4*, level 50-60, middling Gear & Mods). My Lumi's only level 74, Gear 9. But I use her a lot.
Everyone says healers get less important near end-game. So it seems designed for Lumi to be the quicker farm, with abilities designed for early-to-mid player levels. Then, just before healers become unnecessary, your Barriss is now properly leveled and geared, with abilities suited for high-damage opponents.
I will get around to advancing Barriss one of these days. She's pretty far back in line, but if I felt I had to, I could push her higher fairly quickly.
But, personally, I prefer Luminara. Some reasons why:
*Luminara's not a horrible traitor!
*Luminara has better headgear. (Seriously, I call her the "Space Nun". And I want to build a team involving her & Vissas Marr, A.K.A: "Lady Lampshade", + like Leia, Assaj, etc. Call the team "Fashion Shoot".
*Luminara's Ability Block comes in handy.
*Barriss's basic lightsaber attack does about as much damage as a kiss from Granny.
So, Luminara first, Barriers eventually.
