The vast majority of married couples file joint returns, because it’s almost always cheaper.
If you have income-based student loans, however, you might consider filing separately.
These loans are usually based on your adjusted gross income. If you file separately, they are only based on the borrower’s income. You won’t be able to take the student loan interest deduction, but it still might be in your favor. For example, you could end up owning an extra $1,000 on your return, but you’re going to save $400 a month on student loan payments, so it makes sense.