I've been to both and let me tell you, DWA is wwwwaaaaaayyyyy better than the one at Fair Park. The one at Fair Park is like a square building with fish tanks lining the walls. You walk in a big square then you're done. Nothing exciting at all. We were in and out within 10 minutes. I haven't been to the World Aquarium in several years, but when I went, it was really really cool. Yes a little pricey but way worth it...especially if I had to choose between the two. And even though I haven't been in a while, I hear they have made some really great and entertaining improvements.
Hope this helps!