What is Paul McCartney's favorite instrument?

Paul McCartney plays many instruments, a few of which are; guitar, bass guitar, piano, harmonica, recorder, banjo, mandolin, and drums.

Paul's drum playing is most notably heard in the song "The Ballad of John and Yoko", which was recorded by only John Lennon and Paul, without the other two Beatles.
Paul Mcartney played the Bass Guitar, the guitar and the piano. However it is said that he couldn't read sheet music????????