Both are great so it really is a personal decision. Do you have children with you? What are their ages?
When my DD was 3 I chose to go to Typhoon Lagoon and we had a blast! Now that she's 5 we're going to try Blizzard Beach this year.
Friends added the Water Park and More option to their tickets last year so visited both water parks and enjoyed them both. I'll try to find out if they preferred one over the other.