A lot depends on what your child most enjoys. If they want to do the slides but are a bit nervous about going down alone, BB has double tubes so you can ride together. The tot area is not as impressive as TL's, but the pre-teen area is fantastic. BB's Family Raft ride is by far the better of the two.
On the other hand, if your child will do body slides alone or mostly wants to play in the water, TL is the place to be. The wave pool is set up for all levels of comfort, even down to the runoff area where tiny guests can splash in very shallow (and very warm) water.
For pure visual impact, BB is the more creative park. But for lush, tropical relaxation, it's TL hands down.