References previous coworker or manager?

Hey Guys,

I completed my co-op a month ago, and I'm currently applying for jobs for this coming graduation.

I was closer to my coworkers than my manager, so I'm wanting to provide my coworker as a reference. In fact I'm confident they'd give me a better reference. Would it look bad if I use my coworker instead of manager?

Secondly, what are the chances of companies asking for references for previous co-op students going for the first new grad job?

ps. software development position