I say women, because women have more opportunities to cheat, and are better at hiding it because they have more incentive to protect their image.
Men generally believe that women cheat more but are better at hiding it, and women generally believe men cheat more because we are biologically wired to spread our seed. The reality is, both genders cheat at similar rates, especially today. Women were never known to cheat as often as they are today because cheating came with bigger risks and shame. But today women have the same freedoms as men, and naturally exercise them just as often collectively.