I'm from Philly but lived in DC for awhile. The biggest thing that struck me is that the DC metro is so much better than SEPTA. We have two main train services, regional rail, and the regular trains. Regional rail is usually clean but is pricier and has very low frequency. The other trains are typically dirty unfortunately, including the stations, and can be sketchy in certain neighborhoods.

DC seems to pay for much more cleaning than Philly, because it's generally much cleaner.

Crime is pretty bad in Philly right now, probably worse than in DC.