Contemporary, I'd go with Sandy with only six titles. Classic era, I'd go with Chrissie Beauchamp. She was an 80s porn star, pictured on the pool table in the box art. She only did 10 movies. Very pretty. Hard to find.
I'm gonna say Faith (not sure of the last name. exquisitely busty UK teen)
She did a couple of hardcore scenes and retreated back to softcore. Major loss to those of use who wanted to see her bounce & suck...