Ack, how'd I miss this thread?!
So, are you looking to commute to USC, or just looking for a neighborhood that offers convenient access to good riding?
I just commute or ride solo for most part, so I'll let others chime in on the group rides thing. As far as neighborhoods go, it depends on what kind of city experience you're comfortable with. Do you want something that's:
a) Gentrified,
b) Gentrifying, or
c) Cheap? (sorry, having trouble coming up with a third term).
"Gentrified" could be the West Side (gentrified from the git-go!), or some place like Silverlake or Los Feliz, which have seen huge transformations in the past two decades. Eagle Rock has always been a fairly genteel place, and has a fairly long neighborhood history. Highland Park, meanwhile, is somewhere between b and c. It's in the process of gentrifying, but you can still find reasonable accommodation if you try. Depends how comfortable you are in different urban environments. Where in Chicago are you coming from? I just spent a couple of weeks there last year, and it struck me, for example, that the University of Chicago is kind of similar to USC - a private university surrounded by a generally run-down neighborhood. So, if you're coming from U of Chicago, it may be a somewhat similar environment for you. If you're coming from Northwestern, however, that's a much different story.
Feel free to PM me, too, if you'd like. I have lived here for over 25 years, and spent my first 23 years in the Midwest (Wisconsin). So I have a bit of perspective on both places. Happy to help.
Downtown has more and more (not cheap) housing, but would be very convenient to USC. There are a few folks (guys, generally) that I encounter on my commute who are headed past downtown (my destination) to USC. Has anyone mentioned Koreatown or Mid-City yet? Those could also be good options, especially if you're going to be driving to USC. You'd be largely cutting across the morning traffic that's headed downtown or to the Westside (heade south instead of east or west).