At the time of repayment, the Stafford loan will have a balance of 5,125(1 + 0.068/12)^18 = 5,125(1.107) = $5,673.71
At the time of repayment, the PLUS loan will have a balance of 5,125(1 + 0.078/12)^12 = 5,125(1.081) = $5,539.36
Difference = $5,673.71 - $5,539.36 = $134.35
Therefore, The Stafford Loan has a higher balance by $134.35