We (me, dh, ds-10, and ds-1) loved Animal Kingdom! If you go expecting a zoo, I guess you'd be disappointed, but to me it was more like WS in Epcot, but with more interaction and more fun. Our last trip, we spent 8 days and went to AK two of them. We easily could have gone two more days. MK is not to be missed, of course. We also loved Epcot. Neither of our ds' were bored there, but they usually don't get bored very easily at all. MGM, I guess, would be the one Disney park I'd miss if I had to, but I'd hate to miss it. It just didn't seem as "wow" to me, but it was a lot of fun and the show at night (darn, can't remember the name) was just wonderful.
I've not been to US and it's been years since I've been to Sea World, so I can't comment on them.