If you're going for something mostly about the world you play in, the characters, ambiance, ... I wouldn't go to deep with a system. Keep it simple like a d100 basic system or something. Else it will take away from the roleplay and occupy the space in your games. My worst experiences in trpg were with systems with two many steps for a roll, too many rules to keep up with, that kind of stuff. The more time passes the less rules I want, give me a few attributes and skills with a d20 or d100 and let's go!