I've never really thought about it, but I guess mine would have to be 11.
I was born at 11.50 on the 11th day of the 11th month. My Answerbank name has 11 letters. The full version of my real forename has 11 letters. I am a follower of both football and cricket - sports which have 11 players per team. Traditionally, the luckiest number is supposedly 7, which, erm, rhymes with 11 (OK, we're getting tenuous now).
And, of course, as any Spinal Tap fan will tell you, it's one more than 10.