This assumes that we are talking about a single linear measure of intelligence, which doesn't seem to be the case with normal humans. For example the same person can be above average in spacial reasoning but below average in verbal reasoning.

The relevant analogy for this would be social intelligence, so the person you should be the most suspicious of is the person who has displayed the greatest ability to manipulate social situations, though ironically if they are socially intelligent they should be able to prevent you suspecting them.