I'd sell Vanguard taxable rather than the loan. In addition to the interest, I believe some student loans have origination fees which add to your costs. Also the hassle of applying, making sure the proceeds go where you want, making payments, etc.
That being said, student loan interest can be tax deductible. If you were in a high tax bracket (probably not if you're a student, but it can happen) and able to deduct the interest (again, unlikely if you're in a high tax bracket), and that brought the rate down to 2-3%, I'd consider it.