I've taken the Megabus from NYC to DC and back quite a few times. With one exception, the trip has always been very easy- and the exception was simply due to holiday weekend traffic over July 4th. I typically spend the extra money to get a reserved seat. Megabus is clean and provides free wifi and electrical outlets. It drops you off in Chelsea, on 7th ave in the mid-20s.
I like Amtrak, but, frankly, the ticket prices are exorbitant for a trip that is not substantially shorter and service that is not always more reliable than dealing with traffic.
"...everyone finally shut up, and the audience could enjoy the beginning of the Anatevka Pogram in peace."