If by "urban" you mean indoors or where you have worries about overpenetration, then a good 5.56 round from an AR-15 is your best bet. It has the ability to punch through body armor if needed, but will also fragment when hitting walls, minimizing overpenetration risks. It is much less of a risk than 9mm or .45 acp, and most shotgun loads that you would want to use in a self defense situation. This is why many swat teams are switching from 9mm subguns to AR type platforms for dynamic entry work.
In my mind, the classic example of "urban" is Beslan Middle School #1 [see my post at #59 above].