We actually just got back from a waterpark only trip (we are seasonal pass holders and are still blacked out from the parks!). We visited TL, Aquatica and Wet and Wild. We had a great time and were completely exhausted each night.
Now...for the comparison...(we have two boys, 8 and 4, both under 48" and my little one is under 42" for a reference point).
Overall, we enjoyed TL more. If it is atmosphere you are looking for, though, Aquatica is wonderful. The park is very lush and brightly colored. Lots of sandy areas and wildlife. The wave pool is very nice...smaller waves than TL but still lots of fun (and the bottom is not rough like the one at TL). The music played is very tropical and all the announcements are made with an Australian accent which I think adds to the atmosphere! No snorkeling but lots of places to observe the dolphins and the lazy river goes past the dolphin pool and an aquarium.
The kids area at Aquatica (there are 2 actually) is huge and can be a little nerve wracking because the kids can disappear easily. Also, the water slides in the kids area have a height requirement of 42" which makes no sense to me. There are many slides there that our little one could not ride (even the family raft ride which is illogical) and a few that our bigger one couldn't ride (the dolphin plunge is 48" and so is the new Omaka Rocka slide but both are mild and shallow so I am not sure why the height requirement). To be honest, I think that the height requirements at the water parks were pretty arbitrary...some slides at one park were restricted while the same slide at another park had no requirement. Better would be to give a swim test to the kids and issue wristbands accordingly...
Anyway...if you really like TL, I am sure you will enjoy Aquatica as it is pretty and lush. It does get pretty crowded and I think closes to capacity most days but if you buy tix online, you get early entry and can hit the popular slides early on with no wait. The day we were there it was not too crowded but it was a little rainy that day.
Let me know if you have any specific questions!
Jill