I prefer BB for younger kids. In addition to a preschool area (which TL also has), BB has a 'Junior Ski Patrol' area specifically intended for pre-teens......seems like the recommended age range was 5-12 or something like that. We've been to both TL and BB with 3 kids (last year they were 3, just turned 5, and just turned 9), and they all preferred BB. The 9 and 5 year olds both went on many of the bigger slides at BB (even though the 5 year old couldn't really swim yet), and we all loved the family raft ride (which is much better than the one at TL.)
All that said, TL does have some advantages: much nicer landscaping......more tropical feeling, and the wave pool at TL is certainly awesome.
Even considering those things though, our family still votes for BB.
I'm sure you'll have a great time whatever you decide is best for you.