Been to both. TL has a better wavepool and the snorkeling, but
BB is definitely better, especially with a 12 and 13 year old. BB has better, more varied slides, the biggest lazy river I've ever seen, the biggest family slide in the world (six people in one raft) and more elaborate kids' areas. But you'll have a great time at either one.
I can recommend both parks over AK. AK is fine if you've never seen it before, but it hardly rates a second visit. Especially if it means giving up a water park.
We plan on going to BB instead of AK until Expedition Everest is done. Even then, we'll probably visit AK in our swimsuits and head over to BB afterwards.
I'm a huge roller coaster fan, but I'm getting to the point that I like a good water park better. The simplest equation for it is this: How many times did you smile in a given day? The theme parks, whether Magic Kingdom or Six Flags, are a few minutes of major thrills interrupted by long stretches of planning, walking, and standing in line. (All of which I love, by the way, but it's as much a quest for entertainment as it is entertainment.)
At a good waterpark you spend your time DOING, not planning and strategizing. Walk through a well-designed waterpark (which includes both BB and TL) and the smiling to standing-in-line ratio is much more favorable. Less walking around, thrilling slides, relaxing lazy rivers, and a great kids' area where we can get each other wet.
We left this park in a better mood than any of the main parks. And I would swear that, at any given moment, there are more people smiling at BB than at any of the four major parks