This thread seems rather open ended - did you mean most original PUBLISHED adventure, or most original adventure PERIOD?
I thought up a rather (I thought) inventive adventure after the Tome of Magic came out.
I loved the idea of wild mages (and made a rather unusual one). Part of wild magic was the strange and random effects that happened sometimes upon a wild mage casting a spell. That gave me an idea...
I had a wild mage who, based on a wild effect, had fallen in love with... a sofa. And the sofa had been "kidnapped" and the love-struck mage was distraught and looking for adventurers to "rescue" the sofa. (A love-seat, of course).
And it would not be complete without the "Sofaslayers" entering into the picture as a complication later - but then that was something that actually went way back to 1st Edition play and involved a rather dim-witted fighter and some greedy followers.