Most any triple/triples.
My favorite was a ZRT800 with PSI pipes....Horny.
Close second was SXViper with Bender triples.
Third was the thunderous roar of PSI 1500/1800 Triples with PSI pipes.
How could I forget about Rated R(For sale btw - $39,999 by owner in Chilliwack)
I heard a few horny Apex's too, Irmen's was particularly badass.
And the 2 cylinder sled I found the horniest was a 670 UB mod with Jaws pipes and 4" stingers. REALLY LOUD, but when it was singing at WFO it made a beautiful sound!