For people living on the Northeast Corridor especially New York and New Jersey the best way to get to Philadelphia is via train. There is a station on Septa that will take you to the convention center stop and you can enter the convention center from the train station. Below is an article from Frommers Travel.
New York City-Philadelphia, from $31 round-trip
Boston and Washington are
just a little bit too far from New York City to make good day trips. But Philadelphia? Perfect.
There's a cheap way and a fast way to arrive in Philly by train. The cheap way
is to take the hourly New Jersey Transit trains, with a change of train in
Trenton; that takes about 2½ hours each way and costs $15.50 (or $31
The fast way is the also pretty much hourly Northeast Regional Amtrak trains.
One-way trips only take 1 hour and 20 minutes but cost $35-$60 (or $70-$120
To get to the starting points from 30th Street Station, exit the train station
and cross the street to the Blue Line subway, where a quick ride takes you to
2nd Street station for the Old City area.
Visitors from New York should know that high-class dining is a great value in
this town: places like Morimoto, Buddakan, and Alma de Cuba are much less
expensive (and less snooty) than their Manhattan equivalents. Outside the Old
City area, the gigantic food-mall of the Reading Terminal Market, the historic Rittenhouse Square
neighborhood, and the newly-hip Northern Liberties area are some favorites