Both Blizzard Beach and Aquatica have lazy rivers but whose water river is better? That depends on you.
The lazy river at Blizzard Beach is incredibly impressive. It is a big river. The entire trek of the lazy river goes around the entire water park making it a nice long relaxing attraction. There is nothing special about it in terms of waterfalls cascading down on you or anything else, it is exactly what it is supposed to be. A slow-moving river ride.
Aquatica has two rivers. One is not so lazy. That particular river is a fast and somewhat intense rush like a rapid. It is named as such. Getting out once you are in can be a chore and if you miss your exit, you are not swimming back to make it. Go to the next one or take a ride all the way around again.
Personally, this one is my favorite. It's a great rush with water cannons and waterfalls. My 5-year-old has loved this since he was 3.
The other "lazy river" at Aquatica isn't as slow as Blizzard Beach but it is not fast either. It will take you on two paths, one that shows a big aquarium with fish and another that will potentially see Commerson Dolphins.
This is an easy choice for you. If you prefer very slow, Blizzard Beach is 100% your thing. If you want a mix, Aquatica has both.
Food, drinks, and even cabanas are completely different.