I love both so much, both fantastic song writers and performers.
But it has to go to Bruce Springsteen for me.
His comeback in the 2000's has been fantastic, and he is constantly changing his musical style. From very early Springsteen with its heavy Jazz influences, to his big popularity with Born To Run, arguably some of the greatest lyrics and songwriting. Some of the most layered music performed by a band - The E Street Band.
Then he moved onto a much more rock orientated and working man style with Darkness On The Edge of Town, before The River, a fantastic double album with both upbeat and downbeat songs. Nebraska is an incredible album, and its a demo tape he recorded on a 4 track. Then his massive stadium rock album with Born In The USA.
He had a little rough patch in the 90's, but still had some good songs. Then came back in 2000's with a great reunion tour and some really good albums.
Not only that but he does great live renditions of all his songs, varying them massively. And the stuff with the Seeger Sessions Band is great too, good folk influences.
Plus the man can play guitar fantastically and the harmonica too.
Some great examples of Bruce live:
Seeger sessions band:
http://www.youtube.com/watch?v=kuHIGn-ZXJM
Extended guitar solo:
http://www.youtube.com/watch?v=0t2TdQ-d5OA
Born In the USA Acoustic:
http://www.youtube.com/watch?v=XEev8HQUGsc
Plus he works the crowd fantastic, and still puts on some of the best shows of his career at 63 (Happy Birthday Bruce, today!) up to 4 hours long!
But of course Neil Young is also timeless. But Bruce is my favourite.