My ranking is
Magic Kingdom = #1
Hollywood Studios = #2 (Would be #1 if it was just a bit bigger to compete with MK)
Epcot = #3
And last and certainly least (for me) is Animal Kingdom.
I know many love it but I live near an awesome zoo, that puts the zoo/safari park of Animal Kingdom at least on even level with what I have at home. The rides were few and far between with a heavy emphasis on animals that I didn't need.
With that said, I know it's many peoples favorite park which is one great thing about Disney is it has something for everyone. I was told Hollywood Studios wasn't worth going to and it's my #2. The old saying is you can never please all of the people all of the time, but I think Disney feels if you offer enough options then there is no reason to not please all of the people.