Jefferson has to have been the most intelligent, though Madison and TR come close. Cruz is the one prospective President who would give them all a run for their money.
Then again, TR didn’t live his entire life lavishly beyond his means, as Jefferson did, leaving Monticello and his slaves behind to cover his accumulated debts. If IQ could have been measured in the late 18th or early 20th centuries Thomas may well have edged Theodore by a few points. But he was a genius who couldn’t seem to balance his books. Whether he kept his trousers buttoned around the house slaves is open to debate.