If you’re visiting the historical attractions of Independence National Historical Park [1], Old City is the ideal place to stay. It doesn’t hurt that the area is chock-full of shopping, dining, entertainment, and nightlife options, or that it is one of the prettiest, greenest areas of the city.
With the exception of the Bank Street Hostel [2], and a few of the mid-range chains, this can be an expensive area. Rooms tend to fill quickly, especially in summer, so be sure to reserve well in advance.
Links:
[1] http://www.moon.com/destinations/philadelphia/sights/old-city/independence-national-historical-park
[2] http://www.moon.com/destinations/philadelphia/hotels/old-city/under-50/bank-street-hostel