We owe taxes. what are differences between a short term extension (to pay, not to file) or an installment plan?

My husband and I owe about $6,000 in taxes. We cannot pay it in full at this time, but we will have the money by June. Looking at the IRS website I found information about using an extension of time to pay and using an installment plan. How do you set each one up, and which one is a better option financially?