Heterozygous vs. Homozygous — Differences & Similarities

You and your best friend decide to move in together. You are a very neat person, and your home has always been very clean. Your best friend is the opposite, and her home has always been messy. Now that you live together, your apartment is never clean. Your clothes are everywhere and no one has done dishes in weeks. If we apply this situation to genetics, we can designate one allele for being neat and another allele for being messy. Which allele is dominant?