I'd say there is no "strongest emotion." All emotions are equally powerful, but if not expressed often or left unchecked, suddenly there is an imbalance of strength in emotions. I actually read of this in Stephen King's essay, titled "Why We Crave Horror Movies." I don't exactly have his words memorized, but here's a brief summary: There are two sets of emotions that are recognized by society: Pro-Civilization Emotions (Happiness, Love, Loyalty, etc.) and Anti-Civilization Emotions (Anger, Greed, Lust, etc.). Essentially, we have to keep these emotions in control, in order to be in control of our actions. The only problem is that by openly expressing Anti-Civilization Emotions in public, negative consequences soon follow. As a result, people watch horror movies as a safer version of public lynching (A.K.A. publicly killing people), in order to relieve themselves of these emotions despised by society. So more or less, it depends on how well you keep your emotions in check.