Private student loans are, in my opinion, generally terrible. Why? Because their terms and conditions are very inflexible compared to federal student loans and some other types of consumer debt. Private student loan borrowers are typically stuck with whatever interest rate they have (which is often quite high), and they have very little choice about their repayment terms.
When private student loan borrowers experience some sort of hardship or distress and they can’t afford their monthly payments, even on a temporary basis, obtaining any sort of relief from their lender or servicer can be extremely difficult. Deferment and forbearance options are typically quite limited, any change in repayment terms will be temporary (if even offered at all), and default can occur quite quickly once the borrower starts falling behind on monthly payments.