Greatest Songwriter of all time


I was reading the Dylan post and it got me thinking. There are many great songwriters that come to mind, my expertise/knowledge is primarily with rock music. If you could only pick three, what would they be? My vote for best lyrics goes to:

Jim Morrison
Bruce Springsteen
Elvis Costello

Best music goes to:

Mark Knopfler
Stevie Ray Vaughn
Frank Zappa
jeffloistarca
Smokey Robinson
Becker and Fagan
Jesse Winchester
Tom Paxton
Donovan
John Prine
Gil Scott Heron
McGarrigle Sisters
Stan Rogers

Some others for your consideration.
How can there be more than one "greatest?" If the question is 3 greatest, or 5 greatest, then lists are OK.

The Greatest: Dylan
Runners Up: Richard Thompson, Nick Cave, Iris DeMent