BSB has more soul. They stand the test of time more, whereas N Sync kinda has a corny, dated sound anymore with a lot of their songs. Plus BSB, all the members had their roles. N Sync was basically JT and those other people.
Last backstretch boys album came out in 2013, so they win in longevity
Most people only think of them in terms of Backstreet boys/backstreets back, millennium, and black and blue... But there's like 4 more albums after that