Cannot comment on Aquatica as we haven't been yet but from a children's viewpoint (yeah I am a big kid at heart) I don't think any of the Disney water parks are good enough, may be in the minority here perhaps.
You only have to look at the Happy Harbor play area at Sea World to see what can be done better for kid's.
The designers of Aquatica I feel identified an area where things can be improved.
I actually feel water parks in Orlando in general could be much better than they are.
I kind of get the feeling that Typhoon Lagoon and Blizzard Beach are for adults, but Disney added children's areas just for a feel good factor.
Mind you Joshua does prefer splashing around in a pool at the villa so what do I know!
Wet n Wild went once, years ago , haven't been back.
As ever you need to visit the parks to form your own opinion I feel. If I were you I would try Aquatica first, but wouldn't plan too many water park days as it's your first visit to Orlando.
Have a look at photos of all of them, you can view park maps also - it may give you a better idea of which you want to try.