When we first went to Disney, they only had TL and River Country. At that time it was a no brainer.
Last year was the first time we got to Blizzard Beach. We were at WDW a whole week and we wanted to try the one we haven't been to first. We had a great time.
2 days later we went to TL. It didn't feel as fun as it did the last time or as fun as BB. The children's area didn't seem like it had as much as BB either.
Before our trip was done, we alterred our plans to have an extra day at BB because DS wanted to go back. He loved the tobogan runs.
We are going for 4 days this October with one day at a waterpark. DW wife says we'll go to BB, no need to waste time at TL. In fact, one of the top three reasons we're going back this falls is so he can go to BB. The other two rasons, if you're wondering, are 1.
MNSSHP and 2. It's over our anniversary and we honeymooned there.
With more kids activities and more "fun" adult rides, I'd have to say BB is better. What you'll give up is the great wave pool at TL, but I'd make the trade-off.
Hope that helps.