I gotta vote for the bristletooth tangs. My yellow eye kole was constantly pecking at either the glass or the rocks before a failure on my part led to his demise. A true workhorse. My yellow tang does a pretty good job but isn't as interested as he was when he was young.
My hippo tang, on the other hand is useless as far as algae control goes. She pretty much just waits until dinner time, and grabs everything she can.
I have drastically reduced feeding the tangs nori, as I depend on them to help me out in my algae control efforts, but it seems that the older they get, the lazier they get.
I will say that my one spot foxface still does a really good job. He's out and about all day long, picking at the rocks and is still the first at the trough at dinner time. Even eats out of my hand.