At this time of the year I prefer the train even though it can cost a bit more simply because of traffic. But you don't have to take Amtrak. You can take NJ Transit then SEPTA from Trenton. Trains are timed to connect, and it doesn't take that much longer. But the bus may have free Wi-Fi, so if that's important to you, look into it.

You have to decide for yourself what is more important. Lower price and potential to sit in traffic or paying more for a generally better service.

The closer you get to a date, the higher the price of Amtrak. Since you are talking about December, the chances of a train selling out is higher than any other time of year. They sell out frequently in December between DC and NYC so I am assuming NYC to Philadelphia is the same anyway.

NJ Transit from NY Penn Station to Trenton and then Septa from Trenton to Philadelphia is a less expensive but more time consuming train(s) option. They don't sell out but you could end up standing (unlikely though).

Amtrak has WiFi, too, so it's mostly about price vs. traffic.

~Liz

At that time of year there is too much potential for time lost on the bus (bad weather, accident or just plain traffic). I would definitely do Amtrak. If you buy tickets early the prices are lower and do NOT do the Acela - not really faster.

The Northeast corridor line was damaged by Hurricane Sandy. Amtrak and NJ transit share tracks and tunnels.. While train service on this line has been restored, it is not running at the former full capacity. You may want to check out any changes in schedule and then determine whether you would want to take a bus. Avoid the cheap chinatown buses. There are better bus companies that are not expensive. Depending on the day of the week and time of day you travel the traffic on the NJ turnpike might not be so bad. You never know if there will be delays on the train either.
You should be able to see a lot of things in the city center during the time you will be there

Thank you everyone for your replies. Maxima, the buses seem very cheap but I'd hate to get caught in a snarl up on the outward journey especially as I only have a few hours in Philadelphia. I'm sort of leaning towards the NJ Transit route. It is quite straight forward? I've briefly looked at the NJ Transit site.

NJ Transit to Septa is very straightforward.

Oh ... and the Northeast Corridor service has been completely restored. Any lingering disruptions won't affect New York Penn or Trenton, which are the only stations that matter for this trip.

If Amtrak is not running a full and timely schedule by then, I would do the bus - but do understand there probably will be traffic and get the eariest bus you can. (I used to have a client not far from Philadelphia - and in the early am I could do it by car in 1.5 hours - but in rush hour that could easily be 3 hours or more.)

That's great thank you. I'll mull it over and try to make a bus or train booking before the end of the week. Should get the cheapo fares then!

Just reporting back to say that in the end I decided to take the bus and got a return from New York to Philadelphia for $20.00, booked a couple of days before I traveled. The journey took just over two hours on a comfortable bus which had free WIFI. The return bus left about 30 minutes late but that wasn't a problem for me. I liked Philadelphia and I felt it deserved more time that the few hours I spent there. Thanks again to everyone for your input.

I have taken one of the Chinatown express buses several times, and discovered that their scheduling seems to take into account traffic conditions in that we usually arrive within 15 minutes of the scheduled time in spite of horrendous traffic around the tunnels. But I do not know if they stretch their scheduled time due to special circumstances such as winter conditions (we took the bus in the spring or fall) or the holiday season.

It is highly recommended NOT to take the chinatown buses. They have been involved in numerous accidents, some with deaths, and cited by the government numerous times for having unqualified drivers and not following time/schedule rules for drivers or routes.