My favorite is the 7th.
While I was a student at The Curtis Institue of Music I performed in the clarinet section of the Philadelphia Orchestra on ocassjon. When an orcestra member(past or present) passed away, during a rehearsal, the orchestra would always play the second movement of the 7th symphony.
As a performer, while the 3rd, 5th and 9th are so powerful, the 7th will always hold a special place in my heart.