The biggest advantage of a public community college is cost. Class cost is minimal when compared to a university. Other typical college expenses, like meal plans, dorms, clubs and activities do not usually exist. You will be on your own for those things. The facilities at a university are usually nicer because of the lack of funding a community college receives in comparison. You will likely need a car at a junior college because establishments you frequent may not be as close as they usually are in a university town.
Typically, the student to teacher ratio is much smaller in community colleges. It is easier to get personalized attention and assistance, which can result in higher grades. But the quality of professors is not as high at a city college. Budget cuts may effect the variety of classes that are offered or make it increasingly hard to get into the classes that you want or need. Many classes are offered at non-traditional times at community colleges to accommodate students who work full time.
Most community colleges do not have dorms or the social life that goes hand-in-hand with dorms, as they are thought of as commuter schools. There are usually plenty of apartments nearby; most students live off-campus or at home with family.
Many junior colleges offer feeder programs into large, prestigious universities. You can work on your grades, save money and get some general education credits out of the way before you transfer to your dream university; it may be one you would not have gotten into if not for a community college.