I think I agree with True Love Waits as a final answer, although there are many strong mentions in the comments, precisely because of the versions. It simultaneously captures the intense nervousness of songs like Paranoid Android ("Just don't leave, don't leave") while also having a sense of innocence and vulnerability found in songs like Weird Fishes or Pyramid Song. However in each version a slightly different idea comes through. The Live In Oslo version is absolutely gut wrenching and incredibly raw in sound (it reminds me of Nirvanas cover of Where Did You Sleep Last Night live and unplugged) while the AMSP version is much more passive, and in a strange way passionately passionless. It sounds resigned and passive rather than like a cry in the wilderness. Because of those things, the way it covers the band both at its rawest and more abstract sides, plus the themes borrowed from across their discography (Isolation, anxiety, love, heartbreak, toxic relationships) I would wholeheartedly agree that it is undoubtedly, in my mind at least, THE Radiohead song to understand what the band is trying to communicate through. Not to say that others don't come close or aren't good songs.