I have to vote for BB - and I never thought I would ever, ever say that. We had been to TL 3 times and I just wanted to go back. Kids loved it. On the boards I was getting so many different opinions that I just couldn't decide. Then a friend showed me her pictures and I decided to take the chance.
It was fabulous.
Last year when we went, my girls were 7 and 10. There's a section just for 5-10 (or is is 6-12) year olds. It was great. We parked our stuff there and there was a pool, kid-sized body slides and tube slides, and ice bergs to walk on while clinging to netting. And I could sit and watch - it's all contained and open that you can see them. They had such a good time.
The family raft ride is excellent and long (the one at TL is very, very short). The steps are long to get there, but worth it and after we did it once, my kids couldn't wait to do it again (no complaining about steps).
The other water ride they have that won me over was one where there are 6 slides side-by-side (like you do at a fun park where you sit in a burlap bag and go down a slide) - only you are sliding on a mat on your belly. Our family lined up so that we could go together. We had so much fun seeing who would win.
TL is great too, don't get me wrong, whichever you pick, you'll love, but I think BB just has more to offer a 6 yr. old. She's too old for the kiddie section, and the older kid's section is perfect for her.
Have fun,
Cutekatcar