I think it depends on the 5 year old.
If he's primarily into slides, BB is nice because it has a "Jr. Ski Patrol" area with slides and play areas specifically for kids who are too big for the preschool area but too small for the 'adult' slides. Some of the big slides are also accessible to 5 year olds as well. Definitely don't miss the family raft ride....it's great!
TL has the best wave pool, some medium type slides, and lots of sand for digging, castles, etc., so if he's into sand and waves, that may be the better choice.
My kids (DS-11, DD-7, and DS-5) prefer BB, but the youngest is actually happy at either place. Seems like kids that age are o.k. with the stand-in-line and do attractions stuff for a while but then they like to hang-out and do 'less structured' things, but they manage to find ways to do that no matter where they are. (My DS-5 recently chose to spend an hour running up and down handicap ramps instead of riding the kids rides at a local amusement park.....go figure!)
I suspect he'll have a blast whichever you choose! Have a great trip!