Depends ...
I assume you mean the longest since I've discovered her. In that case, it has to be Petra Verkaik, the women who "brought me back" to hourglass, busty brunettes mid-high school. I've been eternally blessed in my love life since. Petra is also not just a looker but a sweetheart in her middle age (did you hear about the *** who "won" a date with her for his prom?). Now if I only had discovered all those curvy, busty brunette Playmates of the '80s sooner!
As far as mainstream models, Leeann Tweeden since she first hit Fredrick's of Hollywood through today. Cindy Margolis, even though blond, was also a hot form of a woman.
If you want to include pornstars, I think Christy Canyon -- the first woman I unloaded to watching a porn -- would still be hot if active today, despite her age. She was always hot as a 30-something when she came back a couple of times.
Not really into any actresses or *********** going back, although a few had more curves. I think Priscilla Presley was always a beautiful woman since I first say her in the early '80s. Can't remember too many more. Lots of page 3 models from the '80s I would only discover later.