If you're currently unmarried and don't have children, your filing status has to be single. If you have a child who lives with you, however, and you are responsible for more than half the expenses of maintaining the household, you can file as "head of household" and realize significant tax savings.
If you're married, you and your spouse can choose between filing a joint return or filing separately. You can even file as a qualified widower if you lost your spouse within the past two years and claim the same tax benefits as joint filers. With all else being equal, joint filers and qualified widowers will pay the least amount of tax.