I would wait and decide when you are in the park - they are available all over the place. There are only 4 major rides, so if you are planning on riding them over and over, it might be worth it. I personally thought Manta and Kraken were the best coasters I went on at any of the parks we visited (Disney, Universal, and SeaWorld).
I went during a very busy time in December, and the line for Manta was about 45 minutes. I went on Kraken and Wild Arctic, too, but I did a tour (well worth the $$ IMO) and was escorted to the front of the line, so I didn't notice the wait times on those.