I think that BB tends to be a bit busier.
BLizzard Beach is also on less acreage than Typhoon Lagoon so it always seems more crowded to us.
BB also tends to be more popular with all of the faster, bigger, wilder slide choices.
However TL has a much bigger and better wave pool and lots of nice slides and a great area for the little kids.
We like to do both, but certainly find TL to be more relaxing.
I would suggest that you get there at opening time and make the most of the early mornings to to all the slides before the bigger crowds arrive whichever park you choose.
Have Fun!!