granted I once was going for a major in animal science ( yet sonehow became a security guard) so I may be a bit biased but I have to go with Animal Kingdom. For me it's the one park that's filled with the most uncertainty, which makes every positive experience magnified.
I love all the parks but in a way I already know what to expect well in advance and for me at least the only real surprises come when a ride you wanted to see breaks down, which tends to be a pretty lousy surprise. In animal kingdom though I never know if I'm going to get that good picture, if I will even see some of the animals in the park. I mean I think I maybe saw the anteater that was near the entrance maybe 20% of the time. So now when I go and I do actually see it, it's elevated and that much more exciting to me.
plus let's be honest, it's way more fun to say "jambo" than "hello"