Based on what Vonnegut tells us in the story, it can be inferred that George is most definitely (and by a significant margin) the more intelligent of the two, given that he is required to wear devices that handicap his intelligence while Hazel is not. It's important to remember that Hazel, though unintelligent, represents the standard for what is concerned average in this world: this is itself a vital part of Vonnegut's satire, representing an indictment against the society he depicts.
Hazel, as a character, is depicted as air headed, someone thoroughly lacking in awareness. Indeed, particularly concerning on this account is the story's ending. Keep in mind, Hazel has just witnessed her son being executed by the State in cold blood, and yet mere moments later, she has completely forgotten what she has just witnessed, filing it away as "something real sad on television." Vonnegut's satire in this story relies on absurdity (Harrison himself serves as the most obvious example of this, as a seven-foot-tall, super-intelligent fourteen-year-old with the grace and body control of a professional dancer). Hazel's absurd characterization, particularly in the ending, is no exception.
On the other hand, Hazel's husband, George, is quite different from her. He is intelligent, but as a result, he has been ground down by the handicaps that he is forced to wear. Not only does he submit before the State's abuse (in the form of the handicaps), he ultimately acts to reinforce it, as we see when he refuses to set aside his handicap in his own home—not out of fear, but out of a sense that the State is entirely justified to force such conditions upon him. In the end, the handicaps seem to have effectively served their purpose where George is concerned, preventing him from thinking too deeply or too concretely, so much so that, like his wife, he too has completely forgotten the horror of what he had just witnessed. After the incident, he continues on, content in this dystopian picture Vonnegut has imagined.