20th of 20, roughly by chronology.
Stepping outside of chronology (which explains the first sentence in the next paragraph), because we're going to see Pink tomorrow night.
This was more fun than I expected. And as I choose my 20th, I'm uncertain, for this is an artist who has never made a bad album, but also never made a great one. There are usually several hits, along with songs that are forgotten when a new album and tour arrives. For this reason, I am very tempted to choose her Greatest Hits package, which eliminates much of the lesser material (and even adds two tracks that aren't just filler but actually good). But she has made two more albums since then, with plenty of songs I'd hate to leave out here. So do I go with the Hits, or do I let the "real" albums represent her. There is also the "problem" that she is such a dynamic live performer that with many of her songs, I'm attached to the live versions rather than the ones on the albums.