It's a hard choice - I think I prefer the theming at TL but you'll enjoy either. DO get there before the park opens and once they let you in, go through and select your base and get your loungers first!
One thing I would say, at BB you get continuous gentle waves- the wave machine at TL does not operate all the time and when it does I'd describe the wave more like a wall of water and when my younger son was four and was wading in the shallow area, he was knocked over by the wave as it came ashore. We soon backed him out so that he was just ankle deep whilst the waves came in but the non-slip floor they have can sting if you land hard enough! So when Miss Tilly blows her horn (!) to signify the start of the waves, keep an eye on your youngest!