No contest. Definitely Universal.
Unless you family does not mind an unkept park and LOVES thrill rides. Then pick Knotts.
We went to both last year and were disappointed with Knotts. My son loves thrill rides though, and had a blast.
DH and I, on the other hand, LOVED Universal! Our son enjoyed it too. (He is 12.)
For those of you in the area you may remember the Cinco de Mayo Fiasco and Melee. A local radio station offered admission to Knott's for $5