The Beatles first arrived in the US fifty years ago today and, while their first few albums featured songs which were simple and shared so many of the same characteristics (The Beatles loved using 'love'), their music only got better with age. They knew that the 'secret' to long term success was to age with your fan base and they did just that, with incredible ease, and, because they were so amazing and their catalog so immense, there is no 'best song' from The Beatles, only hundreds of songs to be played on repeat and used for any occasion.
"Ob-La-Di, Ob-La-Da" The Beatles
"I've Just Seen A Face" The Beatles
"In My Life" The Beatles (I maintain that Rubber Soul is their best album)