Damn, this is tough, like Desert Island Discs, but with CG at the controls – and narrowed down to only one choice!
Generally speaking, music for me is about putting the listener in a different place, pressing emotional buttons.
There's no other way to do this, so I've gotta cheat. Favorite songwriter would still (despite recent decline in quality) be Rennie Sparks of the Handsome Family, for reducing me to ashes everytime I listen to "Milk n Scissors".
And honourable mention to Jason Lytle, formerly of Grandaddy, for writting at least three played-em-to-death classic albums. Again, pressing buttons to get a response – music by numbers – but by 'eck, he knew what he was doing! 8)