My name is Chris K and I support this message. 
These would be my nominations also and in the same order. 
I didn’t think “Downeaster Alexa” was going to get any love but here I am thirding it.
Nomination: Angry Young Man
Combine that amazing prelude with a brilliant portrait of its subject (and imagine - the World Wide Web was still two decades away!), and you get Billy Joel gold.
I already thirded “Vienna” and nominated “The Entertainer,” but then I remembered this song existed and came in to mention it.
I do like “Everybody Loves You Now” (which alerted me to him), but it’s probably too obscure, so I’ll go with “The Ballad of Billy the Kid.”
It’s a toss up between “Only the Good Die Young” and “You May Be Right.”
I was going to pick this as my second choice but the evil OP only allowed one. So I’ll second this.
Here is a clip of him playing two of his best from the 121212 concert (that I was at).
Since I’m cruelly, unfairly limited to just ONE song, I sort of HAVE to nominate a song nobody else is likely to name, and then hope other people nominate the dozens of others I’m thinking of.
I nominate: “Leningrad”
I second: “Allentown,” “The Entertainer” and “And So It Goes,” third “Miami 2017” and fourth “Downeaster Alexa”
And if anybody else wants to nominate “Until the Night” or “Baby Grand” or “A Matter of Trust” or “Big Shot” or “Stiletto” or “Pressure”… I daresay I won’t object
Pretty sure I’m out of nominations, but again, wish I’d thought of “Stiletto.”
No love for Movin’ Out (Anthony’s Song)?
The best will be his last.
That is my favorite but I’m throwing my support behind Scenes From an Italian Restaurant for best.
Live version of “Summer, Highland Falls”
If you don’t think that opening piano licks are sublime, then you officially have no soul.
Just before these two posts, I read the thread and thought to myself, “‘The Stranger’ and ‘River of Dreams’ both deserve to be nominated, but the OP limits me to one. I’d better wait and see if somebody else nominates one of them.”
I also agree with “The Longest Time.”
By the way, OP: not that it necessarily matters all that much, but did you mean “best song” in the sense that the Grammy Awards uses the term, for the song itself as opposed to the particular performance/recording?
Thirded
Re: live versions, can we all agree that if a song appears in Songs in the Attic, then the version of the song on that album is the superior version?
I’ll be the 1st to nominate “Leningrad”. (and agree with all the previous noms)