What is the difference in repatriation freedom between money in an NRE account versus an NRO account?

This is the core practical distinction. NRE account balances, both principal and interest, are fully and freely repatriable to the US with no dollar cap and no special paperwork, because the money originated as foreign earnings you remitted in. NRO account funds represent India-source income (rent, dividends, pension, property sale proceeds) and are repatriable only up to USD 1 million per financial year, and only after you obtain a chartered accountant's certificate on Forms 15CA and 15CB confirming taxes were paid. So if flexibility to move money back to the US matters, route remitted savings into NRE. Use NRO strictly for income that must legally be received in India. The RBI sets and periodically reviews the USD 1 million NRO limit.