It would depend on what you were talking about but I would rather believe in what I am seeing than what I am being told. At times it is easier to see the fine print than listen to things he says as it can make more sense. For example, if I saw that my boyfriend flirts a lot with different women all the time and when I ask him he lies about it, I would not believe. You should look at both sides of the coin and then go the one that makes you happy and satisfied in the relationship.
Our perceptions often cloud our vision. That's when you go to your gut feeling for "advice." We are all quick to lie our way out of trouble. Men are adept at it. Rely on your instincts. Sometimes, they tell us what we don't want to hear. Even a "dummy" knows when they're being lied to. Whatever happens, you'll be okay.