They all make me laugh in different ways.
John, like everyone has said, just had such an intellegent sense of humor, but he seemed a little self-conscious about him.
Ringo was just a loveable goofball.
George had some great quips that pretty much came out of nowhere.
Paul usually makes me laugh because he often tries so hard to come off as 'serious' and 'professional', but you can tell he's not
.
But most of all, I love it when they all played off of each other.