I’ve seen an interview with him about this. He says he finds piano players at restaurants flying into it when they realize he’s there. He says they all seem to figure out that the song doesn’t go anywhere somewhere in the middle and look over at him for an out. He just looks at them, knowingly shrugs with a smile and goes back to dinner. 
“For the Longest Time” because my Siamese cat loved it and I still miss her painfully every time I hear it.
Easily “Scenes…” It’s just to evocative. I’m surprised to see Stranger getting votes. There’s just nothing in that song that stands out. If I had to guess a dark horse, it’d be “The Entertainer,” but that’s not even on the poll.
Also went with Scenes… I remember seeing him in concert with Elton John, and they would trade off so each would pay the song that the other guy was sick of - So Elton did Piano Man, and Billy did… well, I don’t remember what Billy did. Your Song, maybe?
Scenes was my favorite for many years, but I got a little tired of it. It’s Billy Joel’s Bohemian Rhapsody; there are two or three good songs there, but the concatenation of them is unpolished and just gets jarring after a while.
Looks like we have a clear couple frontrunners, and a few others trailing behind. Thanks for voting everyone. This was a lot of fun for me, a huge Billy Joel fan.