My vote was for other.
I've always been most haunted by the murders of Cheri Jo Bates and Georgette Bauerdorf, both of whom were lumped in with and consequently overshadowed by more sensational crimes (the Zodiac and Black Dahlia murders, respectively), even though were was plenty of evidence that they may have been separate incidents. In the Bauerdorf case, it's the crime scene photos that kill me - I really wish I'd never seen those.
I'm also fascinated by the unsolved murder of Elsie Paroubek in Chicago (1911) as well as several other local crimes here in New England that I guess wouldn't fit the parameters of "classic" but which hound me nonetheless.