In terms of immediate impact at the time, 'Help!' had already been out as a 45, as had 'A Hard Day's Night', so I'd have 'Two of Us' at 3, 'Back In The U.S.S.R' at 2, but, at a resounding no. 1, 'I Saw Her Standing There'.
That countdown.....1 - 2 - 3 - 4.....confirmed, in no uncertain terms, that something was about to change and, sure enough, by the end of the year, huge political and cultural changes ('March on Washington', Profumo, Kennedy's death) had taken place both in Britain and America.