On our May trip in 03 we visited BB once and TL twice. Our 10yr old wanted to visit BB again because of the slides - there are more slides at BB than TL, and they are a little more intense. That said, we found TL a little more laid-back and relaxing. There are plenty of water-play areas for little tykes at TL, and the way the Wave pool is laid out there are little cove areas that are protected from the waves where little ones can play. There also is more Shade available at TL than BB. Either way you can't go wrong, just get to your Water Park at opening hours to secure your "home-base", aka lounge chairs in the shade!
Enjoy!