I would vote for Ben. Though Julia was also a very devoted and self-sacrificing sidekick, I agree with Maria_Merriweather that she was mainly hoping for Barnabas to become attracted to her. Also, I always thought she was a bit crazy for putting up with him, particularly in the early days when he was trying to throttle her every five minutes.
Ben's loyalty was more pure; he stuck by Barnabas because he was a friend, not because he expected to gain anything. He knew that by helping Barnabas he was putting himself in danger, but he remained loyal despite threats from Angelique and from Barnabas himself.
ProfStokes