It depends really on what your friends like to do. If you're into clubbing and such, shibuya, roppongi. Shopping? Ginza, the shopping areas of Meguro perhaps? Otaku culture doesn't get much deeper than akihabara ofcourse, but if you've been in Japan for a while I'm guessing these places are already familiar to you..?
I'm racking my brain right now trying to remember the name of the "Obaasan's Harajuku", I went there before and it was hillarious. Don't get me wrong it's not full of cosplaying, emo grandparents but it's very popular among the older generation with a lot of shops selling stuff that was big back in those days. As I got closer to the station I found me and my mates giving up seats to more and more obaachans... Haha