I grew up in jersey and live in PA now. I worked in center city Philly for 5 years and actually lived there briefly as well.
Philly is a really cool city. It's not nearly as dangerous as it used to be. A lot of neighborhoods that you didn't used to want to be in after dark have been developed with new restaurants and modern apartments.
What areas in philly are you looking at? My favorite neighborhood by far is the fishtown / kensington area. Lots of really cool little music venues, bars/clubs, shops, restaurants, art galleries, etc.
There are some really good mma gyms in philly too. I trained at Daddis MMA the whole time I worked down there and loved it. Daddis, Balance and the new Renzo Gracie Academy are probably the best ones in the city. One of my coaches at Daddis just started his own place last year as well. North Star MMA.