It is more advantageous to file jointly because doing so gives you access to more tax deductions and credits than you would file separately.
Most benefits tied to education expenses are granted to couples only when they file jointly, such as the American Opportunity Tax Credit (worth up to $2,500), Lifetime Learning Credit (up to $2,000) and the student loan interest tax deduction (up to $2,500 of the interest paid). Filing separately means you can't claim these items on your return.
Other deductions and credits you can qualify for when you file jointly but can’t access when filing separately, are
Child and Dependent Care Tax Credit
Credit for the Elderly or Disabled
Earned Income Tax Credit
Tax-free exclusion of Social Security benefits
Tax-free exclusion of U.S. bond interest