http://www.complex.com/pop-culture/2013/05/most-underrated-simpsons-characters/

The best of Springfield's forgotten citizens.

Watching the show for as long as I have, I agree about most of these characters although I might place them differently.

I'd rank Duffman, maybe number 1, with Kent Brockman, Gil, Kirk, Agnes Skinner. That might be my top 5. And I would put Wiseguy at number 6 just because he has so many funny lines.