Relevant factors include:
Interest rates throughout the life of the loan - interest may accrue at one rate while the student is in school and another after graduation
Payment options - lenders typically offer loans on which repayment begins immediately; loans on which only the interest must be paid while the student is enrolled; and loans with no payments until graduation or withdrawal from school. In the latter case, the unpaid interest while in school is capitalized (added to the balance due).
Incentives - lenders may offer improved terms based on the student's payment record
Origination fees - lenders typically charge a fee for originating the loan; the fee is added to the principal (amount borrowed).
The total cost of the loan is documented in the Truth in Lending statement, which the borrower should receive when the loan is originated.