I agree about the Keystone. Bring food from 30th Street station in Philly (anything you get there will be better than the Regional café car).
Also, I strongly suggest getting a redcap at PHL, especially because the Keystone line is always long in the station and starts to line up early. The redcap booth is about halfway down the main hall (on the left as you face the angel statue at the end). They will put your luggage on the train cart, give you a time to come back by, and take you down on the elevator and take your luggage onto the train for you. They may even know which way will be facing forward.
The atmosphere, unfortunately, will be the same as the Regional. The Keystone from HAR to PHL is a lovely, quiet train with beautiful scenery and polite people (for the most part). But from PHL north it becomes just another typical train in the northeast corridor.