This question is always painful. You can take the Beatles apart, and you've got 4 talented, respected, legendary musicians, or, you can take them together and you've got one of the biggest names in music history. A musical super-power, if you will. Together they are the Beatles - apart, they are not. In fact they were all radically different, so it's more a matter of taste than anything.
Kind of like asking someone which limb they like best. But if they have a personal preference, that's cool.
Anyway before I ramble on too much, I'm taking to Paul McCartney a lot lately. Not to say he's the best of them, but his music is what I'm liking best of the four as of late (though, admittedly, I haven't really gotten too deeply into the solo stuffs of Ringo and George).