If you can only choose one I would pick TL. My now 6 yo DD likes both but prefers TL over BB. Of course both have the lazy river and kid's areas but BB has more flume rides. There's a few there I won't even ride (I don't like getting my suit up my.....

) I also love the shark reef. My DD was going to try it last time but we hadn't practiced snorkels and she wasn't ready. We plan on practicing with a mask and snorkel (probably in the tub) before we go in Sept. If you do choose BB they have the family raft Steamboat Springs which is really good.
Her favorite thing, and it's only at TL, is the wave pool!

Even though BB has a wave pool too, it's no comparision to TL-she squeals with delight everytime that big wave comes!

And of course, TL has added Crushin' Gusher' which is great (there is a height limit-not for the small ones).
Like the previous poster said, they'll like either one, but I say if you want to swim with the sharks, go TL. Have a great time!