I only ever saw Noland and Lucy... I think. I wasn't that much into the Battle Frontier and did not spend much time there.
For the Sinnoh/Johto Frontier Brains, I've never even seen any of them. I never bothered with the Battle frontier in gen 4 at all.
I'll just go with Lucy I guess... From the Hoenn Battle Frontier facilities the one I spent the most time at was the Battle Pike... though that's not saying much =P