South Philly if you can't afford a nice part of the Northern Liberties or Center City itself. West Philly and Fishtown (north/northeast) are unnecessarily grimy and lame... and dangerous at times. eg: My coworker moved out to 60th St a while back and, the morning after he moved in, he got up in the morning and walked outside to a dead (shot) guy on his sidewalk with cops all around.

You don't have to live wayyy south but can live in the Bella Vista area or something and be fine. My girlfriend just moved out of that area today off of a little side street with lots of families on the block, kids playing in the streets, no noise, Italian Market like 2 blocks away, etc. I'd check there first.