DH and I just got back from WDW and we had a blast at both BB and TL!! The theming at both parks are great, although I'm partial to BB because I love Christmas . . . At TL, Crush n Gusher was great, make sure you try all 3 versions because they are different. My DH loves wave pools and we definitely agreed TL was much better if you like huge waves. DH loved the shark reef for snorkeling, but I'm a freeze baby so I skipped it because it's only 65 degrees!!
Otherwise, we like BB better! Summit Plummet and slusher gusher are much better than TL's Humunga Kowabunga, and shockingly they don't hurt as much. The inner tube slides, family raft ride, and definitely the lazy river are much better at BB, so if you had to go with one park that's the one I'd recommend!!
But if you can do both go for it!! My best tip: be there when the park opens! Since we went in September it was nice and warm in the morning, the parks were empty so there were no lines, and the ground wasn't hot yet so it was very comfortable. We did go one afternoon for just an hour but it was much more crowded and the ground was a little too hot for my tootsies.