@Arizona Dozent: Yes, Lowry Park Zoo has done a big step forward during the last 10, 15 years although I must say not all of the new exhibits are the best of its kind.
I think recommend Florida Aquarium over Sea World is a question of taste. If you prefere shows and rides, the later is better, if you prefer education and biological themed exhibits, then it is the Florida Aquarium.
In ALL of my visits in US-Zoos, I met ONLY FRIENDLY staff. So I wonder what was wrong for you in the Animal Kingdom. Beside, I am not sure if you can see more animals off of the rides in Busch Gardens then in the Animal Kingdom.
@geomorph: Agree if it is a three-day weekend, then the time could be a little short. So it depends what Betsy mean with "a few days". (Btw: I have done Lowry, Florida Aquarium, Sea World, Animal Kingdom (3 times) and Miami Metrozoo in a 10-day-vacation in 2001. Well, maybe a little stressy, but possible, if you can organise yourself).