Lennon and McCartney are considered by many to be the best songwriting duo of the last 50 years. My vote for best individual songwriter, over that same timeframe, goes to Elvis Costello.
He burst on to the scene as a cerebral Punk/New Wave artist, but he has expanded his repertoire into rock, country, opera, pop, and the standards. There is nowhere that he is afraid to explore.
Because of this he has lost some fans along the way, but those of us who have chosen to stick with him have been justly rewarded.
However, if forced to choose one of his records, I still find myself going back to his second, This Years Model, to me, one of the great rock and roll records ever issued. It's one blinding song after another, all filled with youthful exuberance and rebellion. There is not one ballad in this group, and Pump It Up remains a staple of sports arenas, even after over 25 years have passed.