I love them all. It's too hard to pick a favorite.
I could probably narrow it down between Paul and John. I love John's voice so much, but I love some of the songs that Paul wrote a lot more than what John wrote. Although, I do really love Lucy in the Sky With Diamonds, Happiness is a Warm Gun, Come Together, and others, so I might have to give the edge to John.
Although, it just depends on the day and what I'm in the mood for, really.