Megabus

I'm now a big fan of Megabus over the Chinatown buses.

I paid $9.50 for a one-way ticket from NYC to Philly. If you book further in advance, the fares are even cheaper (They claim as low as $1). However, the fares don't ever get up much past $10.
Comparison: Megabus is just as cheap, if not cheaper than Chinatown buses

I picked the Megabus up outside of Penn Station in NYC, and was dropped off at 30th St. Station in Philly. They also had another stop option at 6th and Walnut in Philly.

Comparison: Megabus is much more convenient location-wise on both ends, and saves bus/trolley fares to and from Chinatown.

Megabuses were painted bold blue with the Megabus logo huge across the sides. There were official signs where Megabuses were allowed to park and load. The drivers were in uniform. The driver made an announcement at the beginning and end of the trip (where the bus was going, how long it would take, thanks for riding Megabus, etc). An employee helped load baggage underneath. We drove straight to Philly without any random stops.

Comparison: Megabus is a lot less sketchy than Chinatown buses