Downtown is good.  Lots of choices but prices are higher. Airport has parking on premises and cheaper but far from all the restaurants.

is, I think, the most sophisticated and walkable part of Philadelphia. Art galleries, restaurants, cafes, Curtis Institute of music. Great market/deli called DiBrunos.  But like any big city downtown, probably not a great idea to be wandering those streets too late at night. If you like history, Independence Hall area is interesting and walkable but more limited in other attractions. Enjoy!

Hi Vanessa - you may want to think about staying near Logan Circle (the Logan in particular).  Right on the Parkway, easy and pleasant walk to Art Museum and Barnes Museum (an impressionists heaven).  Also near lots of restaurants and walking distance to Rittenhouse Square and Walnut Street shopping.  Rittenhouse Square (as noted) also is terrific (Hyatt Centric, Kimpton Palomar, Warwick Hotel).  Good luck - spring is a great time to enjoy Philly