In the
DC Adventures Heroe's Handbook there are stats for Superman and Braniac. The stats in the books are for the 'iconic' versions of the characters, essentially the core character. They include notes for modifications for different versions (such as Aquaman with the harpoon hand, or when he heavily used magic).
In that book, Braniac is given an Intellect score (replaces the D20 'Intelligence' score) of 12.
Superman's Intellect is given as a 2. (His strength, on the other hand, is 19)
For comparison, Batman has an 8 Intellect, and Lex Luthor has an 11.
An average human, in DCA, has a 0 Intellect. Superman is about 10% smarter than an average human (your score is added to a D20 roll for checks related to that ability, so Superman will succeed roughly 10% more often than an average person). Batman is 40% more likely to pass an Intellect check than an average person, and Lex Luthor is 55% more likely. Braniac just beats him by being 60% more likely to pass that same check.