I can't resist these parlor games. For the sake of simplicity, I've ruled out the twin tower tandems of Lennon/McCartney and Jagger/Richards.
Hard to narrow it down to three, so how about these groupings?
Songwriters:
All-time, men's division
Bob Dylan
Neil Young
John Fogerty
All time, women's division
Joni Mitchell
Lucinda Williams
Iris Dement
"Alternative"
Elvis Costello
Marshall Crenshaw
PJ Harvey
"Obscure"
Walter Salas-Humara
Freedy Johnston
Liz Phair
"Cult Heroes"
Townes Van Zandt
Gram Parsons
Alex Chilton
Best Singers
Billie Holiday
Al Green
George Jones
Best Guitar
Richard Thompson
Best Growl
Iggy Pop
Best Hair
Flock of Seagulls
OK, somebody want to start a "most depressing bands" thread?