Chicken/Egg - Singer/Song

My current chicken vs. egg dilemma began while developing my summer course on timeless songs. It deepened following the offline response to three Mt. Rushmore posts on that same subject. Then, after recently reading composer Otis Redding's comment about "Respect" never again being "his" song after Aretha Franklin's version was released, I decided it was time to turn this particular headache-inducing dilemma over to you. Please consider the following:
1.) Over The Rainbow
2.) I Will Always Love You
3.) At Last

For #1: Is the first version of this Harold Arlen/Yip Harburg tune - sung by Judy Garland in 1939 - so iconic that the song was destined to be timeless? Or is the song itself so well constructed it would have endured as well as it has for these last 75 years no matter who first performed it? Ringo Starr, even?

For #2: Is Whitney Houston's version of this song - first a country hit for composer Dolly Parton years before - so iconic the performance catapulted the tune into timeless territory? What will happen to this tune if Whitney's posthumous reputation fades a bit? Will others still be recording it 30 years from now? 50 years?

For #3: Is Etta James' 1960 version of this 1941 Harry Warren/Mack Gordon song - also a top ten hit for Glenn Miller in 1942 - the only one that can be called iconic? Was this tune just waiting for Etta to re-discover it 18 years later thus extending its appeal an additional 50+ years?

Singer or song? Six months is a long time to wait to lay an egg, even for a chicken like me.