While the section north of Bethpage is nice the section south is really bumpy. I ride from Massapequa to Cold Spring and generally use the streets with the exception of the path ridge over the Southern State.
Weekdays are OK but on the weekends it's best to avoid the path due to traffic. Nothing like coming around a corner at 18+mph to find some people standing in the path talking.
I still like taking Round Swamp Road for the long gentle up hill.