Typhoon Lagoon wins for me, but just by a sliver. Both water parks have particular advantages:
The reason I love Typhoon Lagoon is that there is an awesome tidal wave pool that I could spend hours in. I will NEVER forget the first time I visited TL 10 years ago, and was in the wave pool, just hangin' with my 12 year old daughter. Suddenly, a whistle blew, and everyone screamed and began running toward shore. Eryn and I had no idea what was happening. Suddenly, this wall of water began moving toward us. We turned and ran, too. The water caught us before we reached shore, and carried us along. From that moment, we have both been hooked.
I also love the shark snorkeling pool, which is only at Typhoon Lagoon.
Blizzard Beach has the most thrilling water slide, some say, in the World. If you love water wedgies, this is the park for you!
There are also more group tube rides at Blizzard Beach.
Blizzard Beach has a fun bobbing wave pool...
I love both water parks - you can't go wrong visiting either!