I'm no expert, but we love waterparks. We did all Disney last year, too. We loved Blizzard Beach's slides, finding them much "gentler" than the ones at Typhoon Lagoon. We really, really liked the wave pool at Typhoon Lagoon and the shark reef swim there.
We are looking forward to Aquatica this year, it looks like lots of fun in the pictures and we are doing Sea World, so we got the two park pass this year.
We have been to Wet N Wild several times, and it has great rides, too. At 8, your youngest it probably too big for the "kiddie" area, but maybe too small for the wildest waterslides.
My 8 year old liked Blizzard Beach, my 11 and 14 year olds liked Typhoon Lagoon for the wave pool.
Suggestions? I say, look into the second day free or online purchase of a 7 day unlimited pass at Sea World/ Aquatica or the 14 day Flex Ticket. The flex ticket will get you Wet N Wild, and I think you can even add Aquatica to the Flex Ticket for an additional fee.