The easiest way out of central NY to PA is via I-81, and it's a pretty drive as well as interstate-efficient. You can pick up I81 at Syracuse, about 30 miles west of Rome. Rt 12 is a decent alternate as well - have done them both.
From the junction of I81 and I78, you can get on PA 72 to Lancaster. It's an adequate road but not a great one. If you prefer the 4 lane divided highways, stay on I81 to I83 and then take I83 and 283 into Lancaster. I83 gets city-type traffic at rush hours, but it's not a terror.
Would you stop in Hershey, PA, on the way? The "Town that Chocolate Built" is a fun stop too.